Tube Amps 101

When Tube Amps amps overheard whispers of

"lets dump that old piece of junk"

in the 1970's

As the age of Solid State had arrived.

Nowhere left to go..........

Overpopulation took over.

How many? 7 billion upgrades?


Turning 65 has never looked more promising....

Classic Tube Amp

 Field Guide & Tube Workshop Planner

The "antidote" for Audio Forum Nonsense & a Religion of "keeping it all original"

I have been safely restoring and enjoying Tube Amps for over 27 years

Here I go.. into how to tool-up and prepare to do battle the Classic Tube Amps...

How to avoid spending on Dud's....

And avoid my mistakes so you don't repeat them but move on with Music....

and towards the future.......

Classic Tube Amp Internet Safari

Your guide to the Classic Tube Amp online jungle

'Watch out for Dodo-Bird Amplifiers'

Dodo Bird Tube Amps are great for Movie props on 40's, 50's & 60's films

or for the life a remaining stash of "end-of-the-world" Tubes that Dodo Bird Amps use.

Yes often one can modify the Dodo Bird amp with similar tubes, but it will never be exact to the original.

Some old Dodo Bird Amps also under deliver in the Musical Departments even with original tubes!

Unlike Lincolns stated "not all Tube Amps were created equal"


Or... if the tubes are more expensive than putting 4 new tires on your Car, red flag.

Be aware that some Exotic Tube Amps may require "expensive" Tubes to work well.

The 300B and 2A3 Tubes, those are about my Limit for what I would pay.

But this DHT Triode World is worth exploring, wonders await in the DHT 211 world

And then you probably need lots of weird Power and Preamp Tubes depending on

how exotic your tastes get for Tubes and Old Amps....

Hopefully not.

Best to drive the normal roads to enjoy simpler Home Tube Amps or Current Production Amps.

Prima Luna, McIntosh, Luxman, DecWare, Rogue, or Kit Amps.

If you spend, spend wisely.

Buying EBay Rust Buckets is not a winning proposition.

Buy restored (a.k.a. molested) amps, but make sure they offer a money back guarantee.

Unless you are good at fixing old Tube Amps and own a Tube tester, stay away from Classic Tube Amps.



If you want to learn how to fix these amps, you have to READ, INVEST TIME and BUY TEST EQUIPMERNT

Now if you want to avoid a Dodo Bird Tube Amp experience,  spend well.

You may just want to challenge yourself to build a Tube Preamplifier Kit?

Be warned again, if you have never built a Kit, buy it already built.

Kits today are not Heathkits, lots of them require far more skill to build.

You can read so many posts of Kit builders who end up with one Channel not working, etc.

And it is almost impossible to help them by Forums and Texting....

The troubleshooter needs to be physically present.





Well this Preamp offers an astounding 2 nanosecond rise time @100 KHz

just beyond belief, the scope trace above shows this amazing slew rate.
































 I now display a few of the "extreme" examples of Classic High Power Tube Amps

You know, everyone wants to see the Honey first, so that you know what you may be, or are looking for

if you happen to hear one of these working amplifiers below, you are in a rare category of Tube Amp listeners

Most Audio Trade Shows lack a Vintage Room, I may change this....

Dynaco MK6's Monoblocks - 120 Watts - Monoblocks

('needs the defunct Dodo Bird - 8417 Power Tubes')

These amps can be modified for 6550/KT88 but will not perform the same unless the circuits

are modified and tested for the same performance as the 8417 Tubes.





Carver Silver 7's - 375 Watts - Monoblocks

Bob Carver the Tube Wizard

Carver to me has always been the Salvador Dali of Tubes.

He shows you things you never expected or imagined were possible

and them builds them and sells them..... remarkable.

Nothing like a Warm Cup of Coffee in Snohomish Washington State.

The legend himself.... He has done it all.

Bob Carver, He loves to do things HIS WAY


Bob even designed "Receive Diversity" FM Car Stereos.... WTF?

Have you ever heard of the Carver MAGNETIC FIELD AMPLIFIER?

Sonic Holography?

FM Stereo Receive Diversity?

Just Google and be amazed (or confused)

Jolida 3000A - exotic power tubes 211A - 200 Watts/Channel - Monoblocks

U.S. assembled Monoblock wonders, these can drive difficult speakers well

so I actually heard these paired with MBL Quart Omni's effortlessly...

The bottom end was cavernous on MBL Quart Omni Speakers

The combination was stunningly superb, it was beyond surreal...

I took Video, will post it here when I transfer it from Hi8

Also got a Free CD

The Jolida 3000A at Rocky Mountain Audio Festival in 2004 were breathtakingly surreal

So I quote from an article on Jolida below:

Although many of the components that go into these amps are made in China, the factory that produces them

is Jolida's wholly-owned US subsidiary, not a Chinese OEM shop.

And, although the components are produced overseas, final assembly, test, and QA

is done at Jolida's headquarters in Maryland.

This actually makes a case for Jolida being more "American made" than some high end brands

Once I heard the Jolida "future" delivered through a pair of Omnidirectional MBL Quart Speakers...

using 200 Watts of Julida Push-Pull 211A Tube Power

The depth, space, air and limitless wide sound stage was incredible

All in a Hot Room with 20+ people and 4 rows of folding chairs

Marriott Tech Center Hotel Windows do not open, hence the rooms were not designed

for more than 4 occupants.

Note: Each person generates around 680 BTU of Heat on gthe average.

Multiply that by 20, add the Moisture from the Breathing, now you get the picture, and the aroma...

Mesa Boogie BARON - 150 Watts - Stereo

Randall Smith's response when challenged by the Wife, to create a HiFi amp, I want one!!!

This amp offers three Power Tube Operation Modes, a tweakers paradise.

Purists will want Triode Mode.

Death Metal will want Pentode Mode.

Undecided will do a Hybrid Mode.

This is the 'tunable amp", ready to Rock the House Down in Mesa Style.

McIntosh MC3500 - 350 Watt Monoblocks

I once saw a pair of these at Sprat Hall in St. Croix's West End

When I worked at the Underwater Range, I was not into Tubes so much, but I never 'forget a Pretty Face!

The Holy Grail of McIntosh Tube Amps, these started a small revolution in "High Power" Tube Audio


Amp Hunter, is that Classic, a GOOD or a BAD deal?

Not all restored Tube Amps for sale are good deals..., but some are just awesome.

Not all 100% original Tube Amps are good deals..., stay away from those with rare tubes

Some old stuff, has one-of-a-kind parts/modules that are critical and without them, the amp needs to be modified

Some as in the DODO BIRD illustration, have one of a kind no longer available Tubes.

Once those Tubes are gone forever the Classic Tube Amp becomes a paperweight

but the ASP-420 Amp above can happily live on a Museum Shelf for display

It is a gorgeous classic design from an age that has passed long, long ago

The good deals are those amps whose Power Tube sockets can be re-wired to accept

an electrically equivalent tube, one example is the 7355 Tube that is a Miniaturized 6L6

Re-wiring the 7355 Socket for 6L6 is simple and totally amazing.... if the 6L6 can fit in the amp.

Tooling up for the Tube Amp Building/Restoration

Read, Read, Research, Post & Ask Questions

If you focus to spend on getting test equipment because you want to go all-in on restoring old equipment

That is the place to start. Without test equipment working on Tube Amps is not a place of strength

A full set of soldering irons (35w, 60w, 100w)

(If you ever need to solder wires to Guitar Pots, a 100w Soldering Iron makes is easy)

Various Soldering iron tips for the different jobs

A great Soldering Iron holder for safety

Safety Goggles, Cut Proof Gloves...

Below is a list of items for any Tube Amp Workshop

Order a few Rolls of "Chem-Wick", you will need this to restore old Tube Amps.

A Soldapult Solder Sucker, for the final suck!

CAIG Labs D5 DeOXIT, D5Fader, ProGold, the BEST!

A sharp needle awl set (to carefully finish clearing out old PC board solder holes)

A long lighted Power Strip for plugging stuff in and a main kill switch for when smoke gets in your eyes!

A PanaVise to hold delicate parts for soldering and assembly of PC Boards.

Metal Hand Reamers, various up to 1" in diameter

Variable Speed Drill and full set of Drill Bits

Electric Screwdriver

Open End Wrenches

Small set of Ratchet Drivers

Stepped Drill Bit for weird sized bigger holes

Metal Chassis Nibbler (for those Square Holes)

Audio Signal Generator

Oscilloscope, 20 MHz is just fine for Audio, 10 MHz works as well.

After all 20 KHz is the highest frequency you will want to see, unless you are lucky at 100 KHz.

IM Distortion Analyzer, an old Heathkit of EICO is fine, this is required to set AC Balance for Minimum IM Distortion.

(not to be confused with Bias please!)

A Regulated Variable 0-500 V DC Power Supply, Heathkit made a good one

A swiveling Lighted Magnification Lamp for close up work

Eye Protection Goggles, if you don't wear Eyeglasses

Anti-Cut Gloves when working with X-Acto Knives and Metal Work

Lead Rated Hand Wipes, to remove Lead from your hands...

Stereo 8 Ohm 100 Watt Audio Dummy Load for amp power testing

Alligator Clips, Jumpers, Hand Tools

Lots of Parts Bins

Assorted 1/4w, 1/2w, 1w, 2w, 5w Common Resistors

Axial/Radial Electrolytic Capacitors 350V, 450V, 500V, and a few 600V

VOM and Analog Meter with True RMS (for Amplifier Power Measurements)

VTVM for High Impedance Tube Circuit Measurements (optional but useful)

Precision LCR Meter, good to have for Speaker Inductors, must have for Capacitor Measurement

Tube Cathode Bias

Using Cathode Bias in a Guitar Amp is not to common these days but in Classic HiFi amps it really abounds

European Designs leaned towards Cathode Bias, for practical reasons, but Fixed Bias delivers more Output Power!

To my ears there is a sonic difference between Cathode Bias and Fixed Bias

Also Cathode Bias usually required matched power tubes, fixed bias is typically adjustable.

Cathode Bias is simple and straighforward, Fixed Bias is more complicated and risky..

Cathode Bias is just about a Cathode Resisor & Bypass Capacitor.

With just two elements, we create a Voltage producing "Heat Engine"

As Bias Current flows through a Cathode Resistor, the Resistor "Resists" according

to the value of Resistance. Cathode Resistors are usually in the 100 to 800 Ohm Range for Power Tubes.

It really depends on the total current flowing, for 1, 2, 3 or 4 Tubes.

You can choose to split each Tube separately with a Resistor and Capacitor.

Or you can design with a Single Cathode Resistor for 4 Power Tubes *Dynaco ST-35*

Or you can split the Left and Right Side Tubes in Pairs, so now you only need

two (2) Resistors and (2) Capacitors vs. (4) and (4) if you individually bias each tube *Mullard 5-20*

It's a matter of creating a Bias Voltage to the Power Tubes, like Brakes on a Car downhill.

by introducing a DC Voltage at the Cathode of the Power Tube, the Voltage that is created by the flow of the current

is called the Bias Voltage of the Tube.

Simple, no need for any extra DC source to produce a Negative DC Bias Voltage as in Fixed Bias.

The Bias Current is a simple calculation of the DC Voltage across the Cathode resistor divided by the Cathode Resistance.

You can find the schematics in my pages, go looking, explore, be curious....

 Tube Fixed Bias

With Fixed Bias, as in having to produce or create a circuit to make a separate distinct negative (-) DC Voltage (Tube Throttle)

then this voltage source is connected to the Power Tube Screen circuit to control

the Tube Current Flow, by setting the Fixed Bias Voltage, you "park" the tube at a specific bias current.

Or you can install a Bias Pot and vary the DC Bias  (-) voltage to set the Tube Current.

So like a Home Water Hose spigot, where You control the flow of water (current) by turning a Spigot (Bias Pot), that

varies the DC Bias Voltage you "control the flow" of the Bias current through the Power Tubes

This DC bias voltage makes the screens in the Power tubes Negative (-) and reduces the current flow through the Power Tubes.

This is why some call tubes Valves, as you can always take a Power Tube

and apply such a very, very negative DC voltage to the Screens and shut the current flow OFF.

This is called Fixed Bias and is the preferred Electric Guitar Amplifier Bias type as it is

adjustable Hot off the rack, while Cathode Bias is not normally adjustable

But there are plenty of clever circuits to make Cathode Bias adjustable, by adjusting the value of the Cathode Resistor.

It gives it some margin of adjustment, and like Fixed Bias, makes for an adjustable Cathode Bias.

But remember Cathode Bias is simpler, as it does not require a separate "variable" (-) Bias Supply Voltage.

In order to make that Bias voltage  you need a "bias Transformer Tap" with a single diode and resistors, capacitor filter.

This is known electrically as a Half Wave Rectifier....

This (-) DC circuit needs to be 100% reliable, or if the Negative Bias voltage should

disappear, it means a catastrophic power tube failure.

Some folks fuse their power tubes for safety. Better blow a fuse than a Tube!

What is the Sonic Difference?

Cathode Bias to my ears sounds smoother, wider, the midrange of the amplifier shines.

While with Fixed Bias the amps to my ear sounds deeper, sharper, more refined, a bit more power headroom.

The lack of a Cathode Resistor under the tube to ground, makes for less thermal noise and one less series voltage drop.

Less parts, simpler circuit, less noise.

With Fixed Bias the Cathodes of the Power Tubes are connected straight to Ground, with no Cathode Resistor

other than maybe a 1 Ohm 10 Watter to measure the DC Voltage and convert to Current by Ohms Law.


Cathode Bias uses Power resistor(s) to bleed off Cathode Current as Heat, by the Cathode Resistor creating the DC Bias Voltage

by just the fact that the Cathode Resistor is conducting and resisting current, creating a Voltage DROP.

Thusly, a new voltage that did not exist is created across the Cathode Resistor.

Hence this is how a circuit element can create a DC voltage at some part

of a larger circuit, by just knowing the value of the resistor and a simple

DC measurement with your VOM, you have 2 out of 3 Ohms Law inputs.

So you can always calculate that third value that is usually Current.

You have Voltage from your VOM = _______

You can read the value of the Resistor = ________

Current ? = ___________, easy peasey....

Measuring Bias Current Directly

Because to measure just Current with your Meter in Current Mode you need to actually introduce the meter

itself, as a series element in that part of the circuit.

Current measurements are intrusive when you are troubleshooting.

As you almost always need to "un-solder" or "disconnect" parts of circuits to measure currents.

So your VOM Meter becomes like a light bulb, with Current flowing in on the Red wire, and out on the Black Wire or vice versa

Current actually flows..... like water.... in and out of a node in any circuit.

A Node, is formed when we connect, solder, jumper... two or more wires to the same point or solder post.

Like tying up Three or Four Boats on the same Pier post, that post becomes the Node.

You cannot really measure current accurately by just bridging a circuit

you need to clip an "ammeter sensor" around a wire to sense current flow.

But most VOM's don't have that clip-on AC Sensor feature, so the need to "un-solder" a connection

to measure current becomes a hassle, and you want to avoid, unless absolutely necessary doing this.

With a current measurement, one leg of the Meter (Red) to one end of that de-soldered connection and

the other Meter leg (Black) to the other side, effectively using VOM as a wire, to connect current flow.

So Current is an active flow of energy like water, but Voltage is the difference in the voltages (pressures) at two or more Nodes.

Always use Alligator Clips and Safety Gloves when working.

Never take Current Measurements by holding and touching a probe, always clip it on when the equipment power is OFF.

Checking for Power OFF is the most critical part of working on Amps, always power OFF first!!!!

Losing a live current path invites the Inductance at that point to fire a spark.... we don't wan't sparks!

Current measurements are ALWAYS clipped-on, never held with a probe, always with safety in mind such as

wearing Shock Proof Gloves as well, when doing all Electrical Work.

 Current now has been given a means to flow "through the AC Current Meter". Unlike DC Voltage readings that are simple "contact" based measurements.

With gloves on you can measure AC/DC Voltages by carefully touching with only [One hand w/ AC/DC Probe], other [Hand away].

Voltage measurements you just bridge two (2) Nodes of a circuit.

Typically opening and closing a Voltage measurement, does not upset the Inductance at that point in the circuit.

Inductors are the enemies of opening a circuit, not closing it. That spark you see when you just pull the AC plug

from the wall with your Vacuum at full tilt, that is the Inductance of the magnetic field stored in your Vacuum Cleaner as it was spinning.

When you "yanked" that AC cord from the wall, you opened a circuit, and the spark is the collapsing "built-up" Magnetic Field going instantaneously to zero in

a millisecond of opening the switch, even microseconds.

So Inductors fire when opening a contact, while Capacitors fire when closing a contact.

Usually in both cases a small spark fires across the contact.....

Never good to open a part of a circuit that is delivering high Current.... always CLIP-ON- Insulated Alligator Clips

with equipment de-energized, OFF.


Always remember to measure both AC and DC.

As the Law of Superposition allows for both AC and DC voltage be present on the same

wire, stud, post, node, whatever your meter probe is making contact with that is reading

Voltages is about.

Ammeter VOM mode (A WARNING)

So often people blow the Current Fuses of VOM's by placing the

VOM in Current mode and bridging a circuit as if taking a Voltage reading and

POW! blowing the Current Sensing protective Fuse, often hard to find

as these tend to fire at less than 1 Amp, often 350ma.... :(

It's always good to have spare Fuses in your VOM Kit, always carry at least

1 spare set of fuses with the meter case.

ShermanAudio Tube Shop 

 Top 10 Tools to have!!!

Items any Tube Amp Shop requires to be operational and a happy place to troubleshoot

you can start your own Home Business, after a few years of home self education

Invest wisely, as when you are taught how to Fish, you Fish for a lifetime.

#1: Tube Amp Troubleshooting Tool

I would own both a Digital & Analog Meter

#2: Tube Amp Troubleshooting Tool

Any Calculator that Powers up and Works is fine

Add/Subtract/Multiply and Divide, first base.

Square Roots, second base

Exponents, third base

If you can write the values and calculate the results;

Home Run!

#3: Tube Amp Troubleshooting Tool

Tube Tester, indispensable, you will be miserable without one at Home

#4: Tube Amp Troubleshooting Tool

If you can't see it, how would you fix it?

#5: Tube Amp Troubleshooting Tool

Non Inductive 100 Watt, 8 Ohm Audio Resistive Dummy Load x Qty (2) for Stereo

Essential for Amplifier Output Power Testing

#6: Tube Amp Troubleshooting Tool

Dual Trace 10 MHz Oscilloscope (Used) you need to see the Amplifier

Power Trace for Distortion (by taking the Amp to the limit).

Essential for "Channel to Channel Imbalances"

#7: Tube Amp Troubleshooting Tool

Full set of Tools & Workbench

#8: Tube Amp Troubleshooting Tool


$35 Craigslist Old set of Speakers for Testing

#9: Tube Amp Troubleshooting Tools

Alligator Clips, Small LED Flashlight and Assoted Small Hemostats

#10: Tube Amp Troubleshooting Tool



Look for online "sleeping sellers" they are out there, honest folk

who price vintage equipment rationally

Just don't pay extra for an 'un-molested' rust bucket, condition like real estate have value

propositions and selling a delapitated water damaged amplifier is not a good deal

You must also research fair market values as just because it's a Vintage Tube Amp

does not $1000 of value create!

And just because someone purchased an old Amp from an estate sale

Does not qualify it to be sold for 10x to 30x the garage purchase price

In fact, if any old Classic Tube Amp is sold for more than

a brand new equivalent Tube Amp, just buy BRAND NEW

or build a quality KIT, you will save time and disappointment

Plus get better sound and reliability.

Below, are two great values today and there are more

 Prima Luna and DecWare

You can avoid the Pain and go straight for the Music



Both are AWESOME budget amps in the $1500-$3000 range

this is the Sweet Spot for a Tube Amp in this decade

If you want to enjoy Tubes at $500, be my guest.

Also there are the Quicksilver Amplifiers, awesome value for the money


Un-Molested pristine antiques may be lucky finds or money pits

If you read "untested", "plugged-in and the light comes on"

"I am unable to test", "I cannot test any further"

"This was purchased at an Estate Sale, untested"


Now be aware that Classic Tube Amps are NOT for those folks who expect speakers to be 100% quiet when

the Tube Amp is idling. The very nature of Tube Amps makes them always have a slight 120 Hz buzz.

The only cure for this is Solid State, where you trade a slight 120 Hz Buzzing for slight Hissing. The subtle noise in Solid State comes out

of the Tweeter/Midrange and not the Woofer. I think that pairing old tube amps with very efficient speakers

may not be the best synergy. A mid efficiency speaker is probably better with a Classic Tube amp. Same goes for

Tube Preamps, they will always have some type of residual noise. As long as you are seated in your Chair, and

cannot be bothered, then it's OK. But if you can hear a steady noise, hiss or buzz from your listening position

that my friends can be mitigated by working the problem and getting the Tube amp/preamp cleaned up.

Photos that show an old Estate Sale Tube Amp powered up, and not connected to Loudspeakers

this is the stuff of Tube Amp Amateurs and Wannabees... How can you tell if the amp works

when no speakers are connected? Maybe the amp is putting out 120Hz Hum, or worse 60 Hz AC line Hum.

When you get the amp, open the box and connect to your speakers, you will soon find out.

 Estate Sale people, just buy to resell, thats it, this is their business, to speculate

The we have Tube Amp Sharks ready for the prey to fall into the trap on sites

I will not mention, that protect the sellers and screw the buyers

I once won a $120 Denon DL-160 Dutch Auction along with 8 other buyers.

I received in the mail a letter with a B&W Photocopy of the Catridge Specifications

and we all lost out. Only to have both Audiogon and Paypal wash their hands.

Then on the Audiogon Chat someoone knew the seller had been ripping people off

and had that person's actual physical address, so I dropped a Pin on Google Earth on that thief's house

I would have loved to have someone put Sugar in that Gas Tank..... :)

Stay away from the:

Sold AS-IS for $2100.00

Sharks who uncover old Amps, then massively inflate prices

I saw an old EICO for $3500!!! Wow, wow, wow.

I would offer the seller $600 for that EICO HF-87 soaking wet

And in the listing photos, I could see that the Metal Can Caps were sliced open

at their bases and not replaced but re-stuffed and left sliced.

Most folks will not notice all of the danger signs from Photos

I do...


I don't restuff Metal Can Caps, I leave them there for the aesthetics if possible

as we can safely install fresh Axial Electrolytics under the hood with Tag Boards

A simple safe solution for those special out-of-production

Metal Can Capacitors with 25V, 100V, 300V, 350V sections.

So if you cannot swing more than $25-50 for a new CE Manufactiring FP Capacitor then just replace them with

discrete parts; safe, sound, & professional, look below....


Some of the old Metal Can Caps can be replaced with brand new JJ Multi Sections

and the original screw holes line up perfectly with the Clamps that are needed.

JJ Electrolytic Caps are AWESOME

Zero Failures so far with 20+ years in the the use of them

They are designed for Tube Amps, they have unique characteristics on ESR and

several of the parameters that Electrolytic Caps contain that make them the superior choice

along with German FT Electrolytics.

Don't believe what you read on Forums, and also don't believe

what you read about the "poisons" of Electrolytic Capacitors on the Sound of the amplifier

that is all Tube Amp Forum rubbish

Also Fresh Metal Can Caps are still available today as the original Mallory

equipment was purchased and is being used to manufacture Metal Can Caps

They often come close to what the original values.

Don't sweat if the original was 20/20/40/50

You can replace with a 40/40/40/40

Just as long as the first section facing the Tube Rectifier is no greater than 60uF for 5AR4

and 40uF for 5Y3. A safe maximum first value for a Tube Rectifier is 30 or 33uF, you can't go wrong.

CE Manufacturing


I often point out how Audio Forums are not the best place for troubleshooting advice.

Here is an example, of how these Forum threads, can immediately go down a Rabbit Hole from the initial response.

The person is asking about his recently serviced tube amplifier blowing fuses.

States that someone who "supposedly knows what they are doing" worked on the amplifiers.

They make audible Humming.

The Fuse Blows after a few minutes.

Then the well meaning responder, immediately asks "What Tubes are being used?"

As you can tell, the first two questions that need to be asked here are the following:

#1 "Did you pay for the Tech to work on your amps? Or was it a favor?

#2 "Did You take the Amps back to the Tech?"

If #1 was NO then #2 might be NO as well.

If #1 was YES then why are you still blowing fuses?"

Once a Fuse blows, the best medicine is to stop using the amplifiers.

Is the correct Fuse being used?

There are Fast Blo and Slo Blo, and it makes a difference

Repeatedly blowing Fuses, in the Hope for the Amps to suddenly fix themselves, defies troubleshoting basics


"What work was done to your amps?"

" What did the technician suggest when they were returned to you, if anything?"

"Did the Technician operate them for a day or two called Burn-In or Soaking?"

"Have you taken the amplifiers back to the Technician (or wannabe) who fixed them"?

"Were any parts replaced at all?"

"Do you have a detailed list, or even maybe a bag of the old parts replaced that you can describe?"

"In a dark room, before the Fuse blows, are the Plates of the Power Tubes turning RED?"

 "Was the Power Supply fully restored, and the Bias supply fully restored and tested?"

"Were all old Power Supply Capacitors, Electrolytic Capacitors and Voltage Dropping Resistors replaced?"

"Is the Power Transformer getting Hot, or Vibrating prior to the fuse blowing?"

"Do you know how to listen for 60 Hz vs. 120 Hz Hum?"

"Is the Hum you describe not a Hum, but a 'Buzzing' sound?"

"Do you have a VOM, and know how to measure a Tube Amp safely?

"Is the Bias Potentiometer Control working at all?"

"Do you own a Tube Tester?"

Then explain how to test the Bias Supply to validate the voltage wiper for proper Potentiometer function

"with all Tubes out of their sockets of course"

KT-88 vs. 6550 should not be a problem in terms of biasing and operation.

Having simultaneouly bad tubes in a pair of Monoblocks is low probability.... but can happen.

Do the Tubes test OK?

Although the KT-88 sounds more aggressive/clinical, I find the 6550 much smoother on top, more relaxed.

This post is the classic "Leading the person down a what type of Tubes are you using" assumptions

The Forum responder, is coming out of the dugout, with no real notion or capabiity to ask the right questions for help

And the well meaning responder without any type of troubleshooting questions gores straight to the "Tubes drawing extra Grid Current"?

 Huh? OMG we have Amplifier ESP at work.....

Obviously showing an awesome amount of 6550/KT88 Tube knowledge allows Forum readers to nod their heads and clap their hands

Folks this is the wrong Yellow Brick Road to take a poor guy with blown fuses who may have

spent good money on a questionable Tech, who may have or have done no work at all.

People, if you need real advice, just send me an e-mail. it is that simple;, I don't bite, don't flame and empathize.

I have helped hundreds across our Planet and met some in Countries I have visited.

But I refuse to post anything on Audio Forums, as I always get booted/written off by the Tube Gurus.

They all have the same Mantra

"Hummmmmm", "Hummmmmmm", "Huuuuuuummmm"


Oh wait, the Amps have to be un-molested, carefully brought up on a VARIAC to preserve

the all 100% Original Parts that are necessary for the amplifier to hold value and sound the best?

Another narrative in the age of the Keyboard Bullshitter

Mr. Paul W. Klipsch would agree...

Just picture a Road Trip, in a 100% original 1980 Vehicle

stored in a barn, with a fresh battery and properly inflated tires.

How far will you go?

Red Plates -"Been there, done that"

The usefulness of a Dark Room

The Tube Power Amplifier - :Danger Zone:

Never leave a powered Classic Tube Amp alone, always be vigilant.

The "notion" of warming up the equipment, while You are away is nonsense

Stepping away for a few is fine,.... just don't go shopping

When unsure turn off the lights and look at the Power Tubes in Pitch Dark

See if the Plates are Red, or have a Charcoal-Ember Center, this means the Plates are above MAXIMUM DISSIPATION

This will wear out your Power Tubes, or worse, can melt the Output Transformer Primary Winding.

The Plates should be pitch dark with no hint of any overheating anywhere.

You should only see the glow of the Filament through holes in the Plate 

If you see Red Plates, turn off the amp and troubleshoot.

You can see this Tube is in TROUBLE!


If you are not there, to sense a burning smell, its probably too late.

Mains Fuses in Classic Tube Amps do not always protect.

Old Leaky/Dry/Swollen "DC" Conducting Electrolytic Power Supply Capacitors

(Electrically Capacitors are an OPEN CIRCUIT to DC in Steady State)

Old leaky Electrolytic Capacitirs can draw enough DC current to melt High Voltage Secondary Wires.

Fuses in Classic Tube Amps, do not always blow

They may not protect against "Slow H.V. milliampere suicide"

Classic Power Transformers are a pain to replace, expensive to rewind

And Dennis "Doc" Hoyer is no longer getting hits on Google?

Dennis was a Master Transfomer and Coil Winder

So my 5 lessons learned over 25 years..... (in the first 10 years)


1. Dictograph 6V6 Mono Amp - Cooked Transformer, left on and went to the Mall, first mishap, I was 13 years old, room full of smoke.

2. Mullard 5-20 Monoblock - Cathode Resistors Burned, I went to the living room for about 45 min.

3. Scott LC-21Preamplifier - Gifted it to my best friend Rick, His brother, insisted it was fine, but I warned Him to change out the FP Metal Can Capacitors

Eventually the LC-21 Transformer Primary melted, the Fuse, unfazed...


4. Harman-Kardon A700 - Not mine, a friends. I warned Him not to use it until I gave it a checkout; His words on the phone were:

"My A700 is not like yours"... but the next morning, I got the call, from his Tech, one Output Transformer primary had open-circuited, OMG!

5. Bartolucci Model V Double C Core OPT - Open Circuited Output Transformer Primary on my Dynaco MK3 Monoblock Clones.

I had just installed Ei KT-90 Type3 Tubes, I was a fool, to use KT-90s. These Yugo Tubes just "Ran-Away", & took out the Bartolucci, I still have the other one :(

I still can remember the fast "Buzz/Pop" that the speakers made when the Bartolucci Primary Open Circuited.

Lessons Learned:

Don't make or repeat my mistakes......

be aware and mindful around Classic Tube Amps

else pay the consequences

Hey, wait just a second, what was that you say; Dynaco PAS Preamps have no factory Fuse?

Yup.. read-on, and enjoy the 25 years of my adventures with Classic Tube Amplifiers

I have hunted Tubes in the following most unlikely places

during my 80% Business Travel days during 2000 through 2009

Santa Ifigenia - Sao Paulo - Brasil

Brussels - Belgium

Castries - St. Lucia - OECS

Costa Mesa - California - USA

Kansas City - Kansas - USA

Dallas - Texas - USA

Santurce - Puerto Rico - USA

My adventures will continue now as I am again, globe trotting.


The Dynaco ST-70 many consider to be a 'standard' among the Vintage Amps

Used to sell for $250.00 in the 90's in great operating and cosmetic conditions

You can still hunt one down, but there is a caveat.

Old original ST-70's have under-dimensioned Power Transformers.

Cost savings has always been a part of the Tube Amp business even back in the 50's-60's

When you see an original Dynaco Amp this is what you are buying:

"A strained Hot Running Power Transformer"

"Old Phenolic PC boards with black overheated areas"

"The 7199 Tube"

"Leaky Metal Can Capacitors"

"Aged Drifted Value Parts"

Plug that old ST-70 amp into 125 VAC and stand back!




Visit my Tube Amp Spa for treating this Classic Amp affliction





When you are smart enough to catch your EL34's Plate Red as you frantically

attempt to adjust the bias, while the old Coupling Capacitors are leaking DC

and the Metal Can Capacitor is conducting High Voltage DC to Ground

You may likely have a leaky coupling cap or a cracked PC board trace, or multiple issues

You will be lucky if the fuse blows, if you use the ST-70 like this for prolonged sessions

The Power Transformer Secondary Winding can melt.... if a tube goes RED

The Metal Can Capacitor can Short Circuit altogether.... POP goes the Religion of Old Parts

Lesson learned... using an old original Tube Amp is like Rowing a leaky Boat

Eventually, you will tire of the problems, or the amp will stop working.

The parts needed to make an ST-70 a daily player can cost just as

much as you Paid for the amp, or even more

Just because you laid down $850 plus shipping does not get you a stable ST-70

Is a restored ST-70 worth $1500 ? You dedice, not me....

Do you know how and where to order the Parts needed?

Can you really restore the old amp yourself?

Have you a workbench with Solder Wick?

Do you know what Solder Wick is?

If you delude yourself into changing a few parts here and there

You may always be in that place where the equipment

acts up more than you would like or want it to.

Save yourself the hassles of being a slave

build a fresh new ST-70 kit yourself, or buy an already built kit.

Parts are new, and the unit will work well for decades.

Also, the 7199 Tube is one of those tubes whose reputation is

exactly what your Google searches return = PITA.

If you see any vintage amps with 7199 tubes, make those your second or third choice.

Never deliberately walk into a 7199 tube situation, its not a happy place to be

also 6AN8 are a close cousin of the 7199, but less pain and still available

Good 7199's are scarce, and they don't sound that good anyhow

Plenty of Dynaco ST-70 Driver Board upgrades exist so when you

buy an ST-70 that sexy old PC board with the fancy red square caps if Crap...






7199 = STAY AWAY

If I ever get another ST-70 to work on, I would IMMEDIATELY order the main PC Board

for a NON 7199 Driver, there are many great Driver Board upgrades available.

Replace the Bias Pots and the Metal Can Capacitor

Get all fresh new Tubes

You will save yourself the hassles of replacing parts on the BROWN PHENOLIC board

that gets like a Chocolate Chip Cookie and the PC Traces get damaged when you try to change parts

My Rant on the popular Dynaco PAS2/3/3x Preamplifier

Most all PAS have poorly performing Volume and Balance controls

as well as toxic old parts that make them sound like people complain that

Tube Amps sound like, muffled, bloated, and tuubey...

You will never know how bad, until you hear a good one and they are musical

The PAS Dynaco Preamps sound amazing when fully restored

They sound idiosyncratically anemic when used in close to original conditions

But some Vintage Tube lovers crave that type of sound, I prefer better.

PAS Preamps sound anemic when 100% original 50 years later, if they

even work at all. Put one of these on an Oscilloscope and look for yourself.

Those two critical parts, Volume and Balance were not designed to last 50 years.

And they affect the Sound in a MAJOR WAY.

The Treble and Bass, they don't get much abuse, but changing them is good for the music

I know, as I built a brand new time capsule Dynaco PAS3x kit from the 70's NIB!

The NOS Volume Control was never used, and was completely bad.

The NOS Balance Control was also bad, never used, BUT....bad, how?

Time, Chemicals and Aging.

It happens to Humans, it happens to Tube Amps.

Carbon Composition resistors usually increase in value over time

Often 30% out of spec.

Coupling Capacitors also chemically degrade

Carbon Potentiometers dry-out and the contacts become intermittent

Lots of the Music just dies across them, never making it out of the wiper contact

When you upgrade the Volume Controls with brand new parts, it is like taking off the

Choke on your old Gas Lawnmower, the equipment "wakes-up".

I actually found a NOS in the Box PAS Balance Control on EBay

Those are RARE.

These are out of production and you CANNOT find them

Nobody makes them, and I even doubt if the original design specs are available

to be reverse-engineered. I would love to get hold of these and have 1000 made

Each of the Dynaco Balance Control Wafers measure differently and have unique Audio tapers that are

designed to work with the resistors on the Stereo Width, A, B, A+B wafer.

Most people just bypass these, and I don't blame them at all.

The real music is in the PAS Gain Stages anyhow so

pulling the chains off is always a great alternative.

The improvements to PAS Preamps are all dramatic when

you know what to look for on a Test Bench.

I am a 12X4 believer and have tried almost every regulated HV

option on the PAS preamplifier, always crawling back to the 12X4

HV Power Supply Regulation changes the character of the music

Some prefer the accuracy, others do not.

In Tube Amps there is no single absolute, we must listen and

understand how every change we make adds or subtracts.

This is the journey we must make to become better

Any Hobby, Subject, Sport, etc.

Classic Tube Amp Lessons Learned;

If you are not safely experienced with Tube Electronics

Buy from reputable used Tube Amp sellers that sell working amps

Even popular Tube Amps has best kept secrets and these are

not always positive news.... so people sell them to push the

problems to others who are unsuspecting new buyers....


Speculation is always part of the EBay Game

Tube Amp hawks are always looking to sell Eye Candy

that needs $500 worth of parts to be safe, sound great and be reliable

Old Tube Amps are cranky

Maybe we need to have Medicare Tube Classic Parts A & B


If you opt for Parts C & D, you can replace the 7199 circuit and

used a 6AN8 in it's place. Medicare will recommend a Doctor who can

perform the circuit modifications to your A700.

So the next time, before you press >PLAY > on that 100% Original Tube

Amp you left on a VARIAC for a week as "Project Lazarus"

Does your Tube Pre/Integrated-Amplifier/Receiver "THUMP" when you move the Sources selector switch?

Does your Tube Amp make a noise on the speakers when you just touch the Chassis (not tapping it)?

Those old silver grounded can Metal Capacitors, do they feel slightly warm or hot to the touch?

You cannot keep your bare hand pressed on the Power Transformer, without feeling pain?

Do you get a small 'ouch-sting" if you touch your operating Vintage Tube amplifier?

Is there even a single, 30+ year original Electrolytic Capacitor in your equipment?

Does one channel, sound louder than the other, with the Balance on center?

Can you clearly see/read, all of the color codes of the Carbon Comp resistors?

HAVE ALL Fugitive "Selenium Rectifiers" been properly replaced?

Can you hear "Hum/Buzzing" from your listening position?

Are any of the tubes, loose in their sockets, not gripping?

Does you Tube Amp sound tired, out of juice?

Are your Tubes, wearing out way too soon?

Does the Phono Input sound lousy?

Do any parts look discolored?

What is NARTB Equalization?

What is Damping Factor?

Been surfing EBay lately?

So are you now ready to explore Classic old Tube Amps

from a down-to-earth hands-on perspective?

ShermanAudio has 26+ years of results and discovery

We help you pick out the best the Forest has to offer

Classic Vacuum Tube Amp Beginners Primer

 If you want to own a Classic Old Tube Amp

You can start your old Tube Amp Hunting Safari at

Antique Stores

$EBay$ (EPay)



Pawn Shops

Used record stores

Used HiFi stores

HiFi trade shows

Ham Radio Meets


Vintage Classic Tube Amps - 101

Welcome to the world of Classic Tube Audio

Where the past and the present coexist in relative harmony..

The first thing any newcomer to Classic Tube Amps must understand

Old equipment requires users to engage, and get off the Sofa

No remote controls, so you need to control your levels from your audio sources

Now think - LP's, Reel to Reel, Reel Demag/Head/Mechanism Cleaning, Cassette Decks

Old tube amps, require regular proper care, occasional calibration and maintenance work

When old components fail, or are simply past their useful life, they become audible nuisances

Vintage Amps are like rare Reptiles & Fussy Orchids, need special owners, who can live with 'quirks'

Old tube amp soft power supply ripple buzz that you hear ... zzzzzzz

When you put your ears close to the speakers...zzzzzzz

Get used to it, or buy Solid State stuff

Learn to listen through faint power supply riple, just like clicks and pops on quiet LP passages

My rule on Power Supply ripple, if you cannot hear it from your chair, don't sweat it

Even the Hiss of Analog Tape;

Analog = Organic = Music

We hear the molecules and electrons working in rare earth metals

Shot Noise... (Google it)

Heck, even exotic old tube Preamps like the McIntosh C20

exhibit "signal bleed-through" between sources

So just turn off all active sources, done!


A good friend of mine, purchased a brand new, out of the Box

Marshall Head and Speaker Stack, I am almost 6 feet and the

Marshall Head Controls were just below my chin.

I was impressed, it was an awesome sight to behold....kneel and pray stuff.

He complained about a faint, almost insignificant buzzzz....

So I visited the "The Stack", and at first could not hear anything

Until I put my ears up to Speaker cabinet grille

The Volume up to 12 O'clock.. 1/2 way

I could hear a very faint 120Hz buzzzzz....perfectly normal for Tube Amps

But He drove the dealer to drink, and got a full refund

He complained  and said:

"I can hear a buzz, when I play softly"

Marshall 100W Stack, playing softly?

Get real, Ritchie Blackmore would say "Piss off"


You need to consider periodic maybe ever 4 to 5 years replacement of Power Tubes

And 10 years replacing the smaller ones

Sometimes you may hear that the Music is not playing as good as it was....

Power Tubes in Classic Amps can also be rare, expensive or Out of Production

 8417 and 7355, these are the Dodo Birds of the Power Tubes

Long gone but not forgotten...

If you buy one of these amps, the modifications to use regular tubes is not trivial

Power Tubes will last a long, long time when they are operated at or below published specifications

Knowing how to determine if they are, is the subject of my website....

If Power Tubes are abused (Classic Tube Amp Hypertension)

they wear out faster, sometimes in less that 12 months

If you don't realize that your Power Tube  Plates are Red

then even once per year, or even faster if you listen often

this depends on whether you are taking the proper measures to control the

Primary Transformer Voltage to your Classic Amplifier

If you don't believe my "Tube Amp Hypertension", Tube sellers will love ya to death!!

When the music goes flat and thin, like an un-seasoned Steak

 your power tubes are probably dying

due to being operated beyond their published specifications

often Classic Amplifier users are oblivious to this common problem

Old Vintage Power Transformers manufactured in the 1950's to 1970's

can BOOST DC and AC Filament voltages way above normal

this slowly takes out your Power Tubes a double whammy


You know when your Power Transformer is HOT and I am not

talking about WARM.... HOT that you cannot keep the palm of your bare hand

of the Power Transformer for at least 10 seconds or more...

Power Supply BOOST issues are double whammy for the un-initiated

You can control that Voltage with a VARIAC or Step-Down Transformer

VARIACS are your Classic Amp friend, but don't think that you will be 'reforming' anything

by using a VARIAC. Also VARIACS can be misused with catastrophic results

Note that Vintage Electrolytic Capacitor reformation is a myth many people believe in.

When Santa Claus shows up at my house on Dec 25th at 1:25am, I will apologize

Proper Vintage Tube Amplifier AC Wall Outlet Voltages should fall between 115 to 117 VAC

Even 120VAC on a stock Dynaco ST-70/ST-35 can push them into early Hypertension.

Also note, that if your Classic amp, does not have/offer a 'Tube Bias Adjustment'

In contrast to Cathode Bias amps

Cathode Bias (not Fixed Bias) requires "Matched" Power Tubes.

Cathode Bias amps are prime for Tube Amp Hypertension Syndrome.

Like High Blood Pressure, it is a silent Tube killer.

A quick look at the Power Tubes in a dark room can tell you if you are burning them out


Dark Center looks like a piece of Kingsford Charcoal

The Red Plate Power Tube above can mean several things....

lets explore this in more detail...

































If your NOS Power Tubes are very worn, they can Red Plate under normal operating conditions, change them.

If your Power Tubes are brand new, they can also Red Plate if they are not operating within their design envelope.

Also some REPUTABLE, tube sellers sell rejected new tubes, and these will often RED PLATE or be GASSY

Vintage Amplifier Tube Hypertension, happens when you operate a Classic Tube Amp

on 125VAC from your House Outlet, not 115-117 VAC

The Dynaco ST-35 is a great example of a Cathode Bias amplifier, that in stock form, does not work at 125 VAC

If you don't believe me visit my TUBE AMP SPA for more details


This one is actually catastrophic, when the Fixed Bias Voltage is absent

Your amp will not survive. Yet once the amp blows up, you can

check with your DC Voltmeter if you can measure anyehere between

 -20 to -45 Volts DC on the G1 (Input Grid) depending on the Power Tube

If that voltage is absent, you have lost your Fixed Bias.

It can be a popped Silicon/Selenium Rectifier, or a bad Electrolytic Capacitor, or both.

Also a bad tube can burn the Cathode Resistor and cause it to "Open Circuit"

 (Shorts are rare across burned Resistors, they usually burn and Open Circuit)

Old Cathode Bypass Electrolytic Capacitors are typical culprits, as they leak DC (a more common ailment)

New Power Tubes, that you just spent $180 for the pair, can be "factory rejects" being resold (not that uncommon)

Also some NOS Electrolytic Capacitors leak DC, so you are always better buying current production.

NOS Mallory, Sprague, Cornell-Dubilier Metal Can NOS Caps are not bargains :(


If you don't have a Local Tube Amp shop to maintain your lovely classic

Scott, Marantz, Dynaco, Fisher, McIntosh, Knight, Sherwood, Grommes, EICO, Heathkit, etc.

You will need someone LOCAL who has test equipment to help calibrate and maintain

The cost of shipping Tube Amps is so high, that it makes it costly to ship out for repair too high.

This also holds true for EBay.

Beware of Sellers that don't post & include proper Shipping Costs.


The next Caveat I have to point out with Classic Old Tube Amplifiers is



This is quite often, the most subtle, but performance affecting aspect

of the typical Classic Amplifier and Preamplifier.

By this I mean overdriving tube input stages and then dealing with the ensuing

distortion across the Amplification Chain.

Put into simple terms, sometimes if we connect a modern Audio Source

such as a CD Player, that has an average output signal level of 2.0 to 2.5 Volts AC RMS

You may inadvertently be creating Distortion at the Input

The GIGO syndrome (Garbage In-Garbage Out)

Nothing that happens to that signal is any good down the Gain Stage chain

This leads the user to have to operate the Classic Equipment with the

Volume Control at the 7 or 8 O'Clock position, as going higher will blast

the user with less than musical sound but even then

The music may sound strange, strained, compressed.... no Bass.

So keep in mind the subject of INPUT OVERLOAD on old tube amps

If your source offers some type of level control, you should lower it to 1/2 and test

Let your Classic Amplifier amplify and do the job.

Back in the 1960's Sources of that time whispered, not shouted as they do today.

If you shout at the Input, the rest of the music will be splashy and strained


GAIN SCALING is another issue we have with separates, by this I mean

Separate Preamplifier and Amplifier

Tubes do the amplification thing very well, sometimes too well

Some Tube Preamplifiers offer more than 20 to 30 dB of Gain

When we really need only 10 to 15 dB of Gain with today's sources

Cathode Followers can also push some serious signals into a Power Amplifier...

Classic Power Tube Amplifier Input Impedances are high, often 250K to 500K.

When we just connect two separates together blindly, we sometimes create a problem.

If the Preamplifier has too much Gain for that combination, you will have to

compensate by lowering the Preamplifier Volume, or if you can

Lowering the Amplifier Input Level adjustment (if available).

When we have very strong input signal and slam the amplifier

The signal will not typically sound good, the music can sound strained.

Then when you lower the input level of your Amplifier, you are also

moving the Power Amplifier -3dB Low Frequency Pole slightly to the right

attenuating the Lower Frequencies

This is in fact almost the same as a soft Low Cut Filter

You can end up filtering out some of the juicier low frequencies, and the end result

is a HOT sound, with a thin low-end

Not the Lush Full Tube presentation that we find fun to listen to at Home.

Classic "all Tube" Receivers/Preamplifiers

and use of an "Un-Molested" Tube Amp

The most fussy of the Classics, the All Tube Receivers

often FM/AM does not work, and they are not simple to align.

Lots of Potentiometers, Cracking Inductors, Panel Lights, Meters, Dense construction

Special Concentric Potentiometers, One-of-a-kind Circuit Modules or weird period stuff like

Maybe even one-of-a-kind Matched-Pair NPN, PNP Sony Transitors in the Phono Stage...

Not all Classic Tube Amps are 100% Tube (Sansui 1000A) Discrete Solid State Phono Stage

Old FM/AM Tube Circuits, often require complete re-alignment of RF sections

when old tubes are replaced the FM Stereo light, may stop working.

Unless you never use AM/FM, so why invest in  Tube Receiver?

If you don't address the RF sections, these can de-rail your Audio if parts go POP!

Like old Tube TV's, sometimes replacing RF tubes did not fix the issue

Fresh new RF tubes may need RF circuit re-alignment

RF circuit 'Q' drifts over time, component drift by heat and use.

Old Tube Receivers are fraught with the perils of damaging one of a kind parts

Out of production delicate plastic knobs, delicate Tag Boards, very delicate wires and cracking parts

Just pulling on old knobs that haven't been pulled in 50 years, can crack them.

Worn out Tube Sockets, like Rectifier tubes "dancing in their sockets not the streets", intermittency issues and

maybe a clearly audible buzz, you can hear from your chair, due to some faulty 0.99 Cent switch

that took weeks to troubleshoot after changing out almost every part, I have been there, done that.

Dozens of tedious to replace grey Suzuki Paper-in-oil capacitors

dried-out, leaking DC, shifting your tube operating points, even the small signal 9 pin tubes

The last remaining Tube Experienced Technicians

They invest Man-Hours of labor, to properly service, making the restoration cost more than the equipment

For example: Fisher 400/500, Sansui 1000/1000A, Pioneer SA-1000, Scott 340B

You would not believe how many small Electrolytic and Suzuki/ERO Foil PIO Caps are dried out...

PIO = Paper-in-Oil

just how many of those sacred "PIO Coupling Caps" are secretly leaking DC, wreaking havoc on the Tubes.

In Vintage Amps, some old parts may look new, and fail with dramatic consequences just as

your Audiophile friends are popping open their third Beer, transfering the Buzz from the Dude to the Amp...

Here is a great example from a Dynaco PAS2/3 Preamplifier

That Holiest of Un-Molested "Sacred Divine"

The inner sanctum of the Dynaco PAS 2/3/3x Preamplifier

The sacred "Selenium Rectifier & Electrolytic Caps"

Very retro to look at, but totally useless today



Parts Cult - The Moonies of Tube Audio

If you ever see the "Cult Members" above, click on Poster

above for a criminally simple & safe replacement

These Selenium Rectifiers make a very loud POP when they fail, and fail they will...

The Paper Covered Electrolytic Capacitors can also POP but can take out the PAS Transformer as well.

This is a photo of an actual PAS Preamp being sold as "Un-Molested"

The only Molested, will be the buyer, when these suddenly fail, and take out the PAS Transformer

There is some type of religious faith thing going on with old parts

I just don't understand it enough to waste my time...

+50 year old Selenium rectifiers all fail, they were never meant to age gracefully, just replace them

Look at those 1960's Paper Covered Electrolytic Capacitors, my good heavens?

Almost as Old as I am, and maybe older

Yet some folks insist on operating their equipment with old parts

so just kneel in holy prayer at he altar of the "UNMOLESTED"

And the TRANSACTIONS to replace burned/faulty parts

The only and only exception I make are

 Museums, Bars or Movie Props

If you have a 100% Original Tube Amp/Preamp

Museum Curators and some Bars will gladly pick up your phone call

and give you an offer to display them... Look at the program "Pickers"

Originality and Museums, Movies and some Bars can do

Classic Static Displays, the true temples of the "Un-Molested"

Lesson here: Never just "plug it in dude"


Also you cannot believe how important Stereo Balance is..

Take the Dynaco PAS2/3/3x Balance Control as a case study

until you are lucky enough to find a good working example

If you have never hooked up your old, un-molested Dynaco PAS Preamp

Or even your Vintage Tube Stereo Amp to a Dual-Trace Oscilloscope (a.k.a. Tube Amp Polygraph)

Feed a 1000 Hz Signal into the AUX L/R, bridge the Audio Dummy Load to your Oscilloscope

Setup a dual trace Ch A and Ch B, 1ms Time Base, align both signals on the screen and...

You may see an dual-trace unpleasant channel to channel imbalance

You never knew was there...

 Hey;  but the Balance Control is at 12 O'Clock dead-center?

You most likely would not have heard the imbalance as most people cannot

I was in that club.... here is my story..


Did you ever wonder, after letting loose and flooring your


Why one speaker blew out, but the other Speaker survived? WTF?

Yup I did that once

 Finlandia 90 proof, Tonic Water and Lime

Listening to Rammstein on Lowthers, on Vodka.... (huge mistake)

"Du hast mich gefragt"; ich bin kaput!

Then paid the price, fried Lowther PM6C Voice Coil...

A700 Harman Kardon Integrated Amplifier I thought was fine...

I then discovered, the Right Channel was 2x the amplitude of the Left Channel...

Balance Control Dead center, Blend on Full Stereo....

The school of High Volume thrills, anesthetized, totally foolish

Why was I listening to Rammstein on Lowther's?

My Mutter prefers not to say..

I prefer not to say.... :)

 The 1-2-3 of restoring Classic Tube Amp, Preamps...

Replace ALL and I mean every single dried-out, leaky, swollen, oozing, looks just fine Electrolytic Capacitor

Do yourself a favor, read about old Electrolytic Caps

It will save you time, aggravation and keep you the non-molested amplifier religion.

What to look for.....

 #1 Most important Electrolytic Caps & Good Tested Tubes:

All 40+ year old Classic Tube Amplifiers

 all have bad Electrolytic Capacitors, period

Good 40 year old Electrolytic Capacitors are Fairy Tales

Especially those sexy, tall and silver looking

Mallory Metal Can FP types

(Hey mama, whassup?)

If you touch the Metal Can, and it is warm

It's leaking DC

and dissipating resistive power (not cool)

Be careful also on old Voltage Doubler Can FP Caps.

One of the Cans is HOT, with 1/2 the DC High Voltage

Hence the Paper Towel like safety covers.

Also before you dive into that buzzing on one channel, make

sure that you have all good tubes.

#2 Power Supply:

Second most important of the Classic Tube Amplifier

Are the Power Supply Voltages looking good?

Upgrade all of the old Carbon series dropping resistors

Of course you dummy, why not.

Resistors are cheap you cheapskate!

Buy the 2% tolerance types

This assures the correct DC distribution.

And when you troubleshoot the DC voltages will reveal

if the amplifier circuitry is drawing less or more current than normal

Don't sweat the Carbon Compositions, these are old school

Use new Metal Oxide

#3 Output Transformer:

Is the dominant factor of how a Classic Tube Amp sounds, not the Tubes.

All transformer coupled Push-Pull amplifiers use an Output Transformer

And the Output Transformer affects how the amplifier sounds... more than any Tubes can

#1 and #2 are fixes, but #3 is just FYI, not much you can do

You are basically along for the ride with a Classic Push Pull Tube amp.

#3 is just part of the Amplifier itself, but.... to get the best sound

You have to learn to live with how it sounds.

And Classic Tube Amps are not 4 Ohm lovers, they require

a different type of partner for a sonic long term relationship to "blossom"

This is where owning more than one classic amplifier comes into the Hobby

You can eventually settle down with the one you love best

usually has to do with the Output Transformer performance and

how your ears perceive the music...

Now about the Tubes

Notice it's not first on the Classic Amp list?

Oh... give me NOS Tubes, or give me Death

"Thomas Pain"

NO AMOUNT of Tube Rolling will make your amp significantly better

So save your money on the restoration, Tubes are the final aspect of any restoraiton

Just make sure that as you restore, you are not using a bad old tube

Some old Tube Amps sound OK, but not as good as others.

please don't start down the Tube Roller Rabbit Hole by splurging on expensive tubes

Spending on shady NOS Tubes, will test your financial sanity levels.

Imagine buying Used Incandescent Bulbs?

Get the picture?

Focus on using BRAND NEW fresh tubes

Like Crispy Lettuce and just picked Strawberries

A return policy in case they are duds...

Never a $300 NOS 12AX7 EBay Telefunken

those Tubes, they come way, way, way later

 Most of the NOS tubes are impossible to determine if ever used

Unless the original Cellophane is intact, and then some...

You can often look at the Pins to determine usage levels...

There are a few honest sellers of NOS Tubes I have purchased from

over the last 20 years, honorable folks who know Tubes inside and out.

Brendar Biever...

Jim McShane...

Brent Jesse...

There are a few very clever people on EBay

 who can fake anything...

Even cellophane wrapping...

I have been burned by Noisy used NOS Tubes from EBay

 and hope you avoid the same experience

EBay is not a good place for used tubes, it's a lottery.

New tubes, go for it, EBay is a great spot.

The worship of old NOS Tubes does two things;

Some sellers sell questionable used tubes.

A few buyers pay a premium for them.

Used Tubes = from reputable sellers

Else walk away...

Used tubes are like used Cars

No real way to know their true history...

Not even a Carfax has a full story that accounts for the

Teenage Joy Ride Dukes of Hazard moment

Cracked Chassis, deformed Uni-Bodies, Moonlight Cousin Joey Repairs...

You win some, and lose more than you win with NOS tubes...

It's like Coin and Stamp collecting.

How do you know that those XF Mullard EL34's did not

play a few "red-plate" Gigs at the "Rusty Hinge"...

Then back into the original boxes...

My final WHITE TOP on Vacuum Tubes

As soon as they arrive, test them, test them, test them.

Don't put them on the shelf, test them.


Also.. "Milky White" Tubes have lost their Vacuum

Be aware of the silent EBay Tube Seller with White-Tops

who have no idea what they are selling

These are, at most, well meaning good sellers who "hoard-to-sell"

Gobbling up Tube Caddies at Antique Stores and Flea Markets

But know zero and resell them

Look at the "White Top" EL34

That nice EBay sleeve of 5 Tubes with one "Whitey"

My White Top Sleeve of 5 Formula Calculator

5 (Tube Sleeve) - 1 (Whitey)  = 4 (Tubes)


When you use fresh brand new tubes






When you use shady old used small signal "NOS" Tubes, the Amps may sound smoother to your ears

You just may be listening to that "worn out" Tube Sound

It may please, but is not how your amp can truly and really perform and sound

If you prefer Color vs. Accuracy, that's fine

As Power Tubes Age, the sound will also change

And patience is virtue here

When new Tubes break-in they settle down.....

Constantly rolling tubes is not a winning proposition

You may never be able to actually allow the tubes to settle down.

You can risk and keep using the old NOS stuff, it can work for a few month's, maybe a year

Just don't place the blame on New Tubes and compare to Worn tube sound

You say: "Ahh those new tubes sound so strident, so shrill"

Especially after #1 and #2

Tube NOS tube rolling becomes Religious, Fanatical, OCD, Audiophilia-Nervosa

If you want to make your amp sound accurate, pay attention to #1 and #2

Tube rolling comes after you restore your Classic amp and have gained

experience on how to pull and push them into their sockets.

Put your funds into the restoration, not the Tubes

Then enjoy... the rest of the Hobby

Why does it happen, because it happens,

"Roll the Bones"

Then later make it happen,

"Roll the Tubes"


Class, now repeat after Me...


Capacitors like Batteries, wear out, with the risk of explosion

Not blowing the primary Fuse

 but burning out, Power Transformer HV Secondary windings

Or if lucky, the Rectifier tube

Check old resistors for drift & overheating

Teacher says "expensive parts are not always better"

Restore your amp with normal parts

Then like spices, selectively swap out Coupling Capacitors

You maybe surprised by that $45 capacitor vs. the $3.50


Replace ALL voltage dropping Resistors & Rectifier Diodes

Don't be a cheapskate


If you have an Output Transformer with 15KHz upper HF limit

Don't expect Supertweeter miracles to happen, they will not.

There was a time, when 1950's Hi Fi was 40-15KHz

Not the 20-20 KHz we all know about

Be aware, if your ears can decode > 15 KHz upper frequencies

If an the amp is rolled-off at the top, don't blame the Tubes right away.

The older our hearing, the less relevant the HF quality of the OPT becomes

40 Hz to 15 KHz is just fine for old Male Boomers like Me...

Female Boomers, you get a Hall Pass, you are probably good candidates for 17 KHz and below.

McIntosh, Fisher, Scott, Harman Kardon, Pioneer, Kenwood

Grommes, Knight, EICO, Heathkit, Luxman and Dynaco

All good Output Transformers

Think of the Z-565 Dynaco

Being pulled today and sold on EBay separately

Those originals, have a sparkling top end!

Acrosound is another Wonka Golden Ticket

Hashimoto,Tango, Bartolucci.... the list is not that long.

Electra Print.....


Classic amps are about enjoying the 'their flaws' in proper context

Consider this if you think old Tube amps will deliver Magic

that is not what Classic amps do...

Classic Amps take you back in time, like that old MGB or Triumph

The MGB smells, shakes, rolls and brings you the thrill of a times gone by at 60 MPH, 4300 RPM

The tappets clacking away, the Gears and Drivetrains making their sounds

The aged aroma of old seats and British Interiors

The guy below is enjoying Deep Purple at 200 Watts

I hope He has hearing protection.


"The Tinder Classic 35W Tube Amp Partner Search"

Best Tube Amp Tinder Hookups > 16 Ohm Six Pack "Sugar Daddies"

The Tinder Hopefuls > 8 Ohm Millennials

Those kinky Tinder Genners > 4 Ohm Gen X and Gen z "alert"

Conclusion - Classic Amplifier Best Sound

For the best overall musical performance it is best to step up a clean low noise audio signal

starting low and the input and allowing the cascaded Gain Stages

to do their job, cleanly without distortion to re-create the Music we all crave.

It will save your ears and also make for a better musical experience

When Gain Scaling is done properly, the Musical aspects of Classic Tube Amps will shine.

Vintage Tube Stereo post Y2K

I wrote this section circa "2004-2005" when I was knee deep in Tube stuff

Also troubled by Audio Forum BS, and no longer visit them for at least 10 years.

Audio Forums make me sick, and I stopped visiting and posting, too much Hate

not enough Education and too many Keyboard Bullies who nurture negativity and bullshit.


Note: Many of the weblinks below no longer exist, but I leave them as they are part of my History and exploration...

I could start this web page by saying that Tube amps are better than Solid State, that tube amps possess some kind of "Mojo", yet I begin by stating that Solid State technology does have many advantages over older tube technology, and one of these advantages is ease of ownership.

In my humble opinion, tube amps went slowly away because of the inevitable fact that new technology displaces older technology. Not because of the equipment reviewer's article or expert opinion on musical prowess.

It is not fundamentally due to sound quality or that transistors are better than tubes. Any designer can work magic with a tube or a transistor.

It's just by the way things work in our modern economies that newer technology displaces older technology.

This is mostly valid except for one particular medium, Vinyl records.

Here we have today an old technology that still appeals to young and old alike. LP's have many new users that rage about the resurgence of LP's, Phono Preamps and Turntables. In my humble opinion the only reason for this is the MUSIC itself.

Some people simply prefer the Analog way and attest to the superiority of a purely electro-mechanical method of sound transcription. Mind you, a wiggling stylus in a dirty groove if far from most people's idea of Hi-Fi. Yet the lowly turntable and the LP are coming back in a way that seems to upset many people who swear that CD playback, SACD and HDCD are king. As a side note the quality of today's pressings varies and just because the LP says 180g Vinyl is not a guarantee of good sound. Recently I purchased a Diana Krall LP that is noisier new that some of my old 70's used LP's.

Here are some basic ideas about Valve/Tube amps as I see them; 

Tube equipment requires user maintenance and user involvement. This is not only limited to eventual tube replacement, some also require periodic adjustment so you have to know how to use some electronic equipment like a VOM. 

As tube amps are more 'organic' than their solid state counterparts, they can become a nuisance for inexperienced owners. The unknowing and non-understanding can easily cause damage to any tube amp or preamp by turning adjustment potentiometers, despite their best intentions.

Tube technology requires that the user have a special "competence" level unlike any other form of modern transistoria (hey, a brand new word!)

Now add to this the fact that new tube amps today are almost always, watt for watt, far more expensive than their solid state counterparts. The idea of using and operating any vintage tube amp may only seem like an interesting proposition to a few. But as I mentioned before, if a new tube amp can test your will, a vintage one can make you believe that all of the common notions about why tube amps became almost 100% extinct just a decade ago were and continue to ring true.

I find it curious how people think "expensive" when in today's dollars there are lots of tube amp bargains.

  1. Tubes wear out, need periodic maintenance and eventual replacement. After all, they are a cousin to the common light bulb, Lee DeForest can vouch for this.
  2. Tube amplifiers need space to breathe, cannot be 'tucked-away' inside fully enclosed audio furniture w/o some type of forced air ventilation
  3. A brand new tube amp is almost always a better first choice than an old fixer-upper amp, unless of course it's free, estate sale or abandoned.
  4. Tube amps don't sound good with just any random loudspeaker solution, careful matching and pairing is required for best sound
  5. Watt for watt, tube amps have typically lower output powers and higher output impedances, unless your wallet has unlimited funds.
  6. Some (but not all) tube amps exhibit low damping factors that affect low bass reproduction when mated with the incorrect loudspeaker system.

Where would I start if asked why tube amps sound the way they do ?

I would say one needs to understand what is meant by an amplifier's 'damping factor' and another is the understanding of the specifications of an audio amplification circuit.

Tube amps sound different than solid state, they do and I can almost bet that this is a fact. The reason why has to do with the way in which the electrons are shaken and the music is delivered to the speakers. But the overriding technical reason why tubes sound different than transistors has to do with their Power Supplies.

I could probably say with almost 99% certainty that all Solid State equipment uses some form of Voltage Regulation in their power supplies. The other way around, 98% of the tube Power Amplifiers out there do not use any regulation in their High Voltage power supplies, or filament supplies.

Power supply regulation is probably the most sonically affecting thing when it comes to powering tube amps and tube preamps.

A typical tube amp requires DC voltages on the order of hundreds of volts, while solid state amps will have DC voltages around 40 to 120 Volts DC. Also Solid State components are complementary, tubes are not. So if a designer needs 400 Volts of voltage headroom in a Power Supply, a solid state power supply is easily designed with +200 and -200 VDC rails, giving the 400V envelope.

Tubes on the other hand can benefit from these types of supplies and often do when in Balanced Configuration, but typically tube power supplies are designed with no regulation and have output voltages on the order of +250VDC to +550 VDC.

Generally speaking, solid state amplifiers can control the delivery of current to a the speakers while typical transformer coupled tube amps swing voltage around the place while keeping the current draw from the power supply relatively constant.

Solid State equipment almost exclusively uses regulated power supplies, while tube amps, employ standard un-regulated DC power. This fact will have a pronounced effect on the sound quality of these two amplifier types, and somewhat the reason why tube amplifiers sound the way they do. Power Supply regulation makes a very big difference in the resulting sonic signature of tube power amps and preamps.

I built an Aikido preamplifier that has switchable 3PDT option that offers regulated and un-regulated power at the flick of a switch.

The difference between both modes of operation is amazing and clearly audible.

Almost 95% of the time, regulated B+ operation sounds much better, tighter and with more definition.

The Un-regulated mode sounds softer, rounder and with less definition.

The other reason why tube amps will have a particular sonic signature is that they employ very small value capacitors in the signal paths.

Transistor (Solid State) amps require by the very nature of the Silicon based devices employed, much larger value electrolytic coupling capacitors that also affect the musicality in a detrimental way.

Unless expensive Electrolytics are employed in the Signal Path, these are well known among the audiophiles, with brands like Black Gate or ELNA.

Smaller value film type caps have less of a detrimental effect on the signals while larger electrolytic caps tend to impart non-linear behavior on the musical signals due to the electrolytic chemicals and the nature of the way in that the electric fields are stored and conducted.

Today we have a new breed of "Output-Transformerless-OTL" tube amplifiers that sound simply amazing. These amps are as transparent as Solid State and use only Tubes and solid state regulators to better control of the voltages required.

OTL amps can provide the speed and weight of solid state with the delicacy of a tube amplifier's air and midrange bloom, when paired with the proper speakers, otherwise they can sound thin and forward.

Yes , it's a brave new world out there, and tube technology has managed to survive thanks to musicians and nuts like us who enjoy this as a hobby.

If you follow the link below, you can read more about damping factor, a very interesting subject, the rest of why tubes sound like they do is waaay too subjective to even attempt to describe, I will not go there.

Comparisons of tube vs. solid state sounds are subjects I would best not get involved in.

But subjectively, I for one prefer mostly tube sound, but also love a good solid state system.

My ADCOM 100 watter still makes wonderful music to my ears. For me it's all about quality and the design, the rest is mostly hype and a mind full of pre-conceived notions. There is a book called Audio Reality now available in PDF from Transcendent Sound. In this book audio myths are explored and picked apart. Some of the statements I can agree to, yet the author makes other claims I find a bit difficult to stomach.

Yet one thing stands out, it is far more dangerous to have many mis-informed people claiming that inductors in the power supply slow the sound down and other ridiculous statements based on the non-understanding of Electrical Theory.

The only way to be able to understand all of the hype and lies is to educate oneself in the basic of Electronics, Power Supplies, Ohm's Law, and Circuit Design.

Once these principles can be understood, a clearer picture emerges and all of the hype crumbles away.

I mostly feel that the audio arts are polluted by some people's sense of wanting to hear a difference.

And once a person convinces himself that a $1000 power cable made the sound more extended, this helps the cruel salespeople who market "Timex Clocks" to improve the sound of a music room by simply putting the clock in the same area. This same company claims that they can improve the sound of your system by sending tones over the phone line.

This nonsense is really disturbing, and those Clocks aren't cheap !

If you read the article on Damping Factors and look at some classic tube amps, often some means of adjustment for the amplifier's damping factor was available in hopes of achieving a better match with a particular speaker system and attain better control of the woofer's cone motion and back EMF. Other designers actually provided terminals strips where one could experiment by installing different value resistors to adjust for the different loudspeaker systems effect on the amplifiers power section.

This adjustment was trial and error at best, and was often described in the users manual with a list of resistor values and recommended loudspeaker systems. You see, tube amps require a small education in order to get the most out of them. They are probably never to be considered plug and play, unless you buy a current production model that employ's new circuitry to compensate and provide most of the music with little user intervention.


#1 - " Ye shall not apply power to a Tube Power Amplifier without connecting a cheap speaker or Audio Dummy load to the speaker terminals " 

#2 - " Ye shall not swap any tube without first consulting a tube substitution manual to verify it's type, application and suitability "

#3 - " Thou shall not covet any piece of Vintage Tube equipment brought to you for repair, adjustment or calibration "

#4 - " Always replace all frayed or crispy AC Power Cords on Vintage Tube amps, regardless of belief or compulsion to originality/religion, if the cord is still pliable, OK to keep "

#5 - " Thou shall always replace all Old power supply FP Metal type can capacitors or electrolytics regardless of origin, looks, originality or belief in the supernatural "

#6 - " Thou shall never leave a Vintage Tube amplifier "Powered-ON" un-attended no matter how much you believe in warm-up time while away at work, tubes are meant to be enjoyed, not left alone"

#7 - " Never believe seller claims that a vintage Amplifier works great if there is no money back guarantee and a rust bucket set of photos "

#8 - " Always test/replace all Vintage signal Capacitors and test/replace all Ceramic Disk signal caps where practical; chemistry and time are not kind "

#9 - " Thou shall never bypass an "Estate Sale" you become aware of, no matter how insignificant it may seem, there just may be a Tube Amp looking for adoption "

#10 - " Support your independent internet "Tube-Sellers" who take the time to properly test, match and grade tubes. Be careful of the large marketing machine online tube stores"

Over the years of enjoying music and audio equipment, lot's of experimentation has led me to conclude something unique about what would I recommend as an absolute first step into the wonderful world of tube audio. What I propose may sound totally heretical. I have reached the conclusion that one should start with the best Tube Preamplifier and mate this to a high quality Solid State amplifier capable of least 60 to 150 Watts into 8 Ohms resistive load. Yes SOLID STATE..... ughhhh, but hold-on, let me explain.

There are some reasons behind this and I will try to convince the skeptics and tube purists.

First, a tube preamplifier is a good way to enjoy the sparkle and air of tube sound, I have to recommend the Transcendent Sound GROUNDED GRID preamplifier, the best KIT for the price, sonically speaking. For the more adventurous soul's we have to mention the John Broskie AIKIDO preamplifier design. The AIKIDO is a special topology that cancels power supply noises and auto-balances triodes. It sounds far more articulate than the Grounded Grid, but the differences are in the Power Supply. An AIKIDO can be built with a super power supply while the Grounded Grid has a lightweight design. Often people call the bass wooly, I say the bass is not really all there at all (heresy!!!) I built, listened and enjoyed the Grounded Grid preamp for several years. I sold it and built an AIKIDO. A Dynaco PAS2/3 can sound amazing, but almost never in bone stock condition. The Volume and Balance pots were and still are cheap bottom shelf parts. I would always replace these two controls with the best you can afford. Most of the magic of the Dynaco PAS preamps is completely lost in 50 year old Volume and/or Balance pots. You would be concerned if you scoped-out a stock PAS, the channel imbalances are the first sign of trouble, followed by attenuated highs and muddy mids.

I have grown to dislike old tube amp sound, when I can hear upgraded versions of the same amp/preamp kick some serious rear end (booty).

So where does that lead us today? Many nice choices.

Preamps are much easier to use for a tube amp beginner than a tube power amplifier. Preamp tubes are far less costly (9 pin types) and good tested one's can be found from a myriad of internet tube stores. BUT you absolutely positively need low noise preamp tubes. If you don't get low noise preamp tubes, your music will ted to have a 'haze'.

Secondly using a higher powered, high quality solid state amplifier will eliminate the necessity to look for tube compatible speakers, allowing the hobbyist to use existing low to medium efficiency speaker systems (Bose, AR, etc.). High power at the amp stage will free the hobbyist from having to worry about deficient bass performance, damping factors and other tube power amp to speaker interface issues.

Getting 100 watts or more from any tube power amp is typically an expensive proposition. Therefore I have to safely say that as a first step look for a nice used ADCOM GFA 545-II or an equivalent Cambridge Audio, Krell, Hafler, etc.

Heresy to say the least, but a reasonably perfect approach to sample the sound of tubes.

What PREAMP should do I buy ?

One can use a Vintage Dynaco PAS series types, or a new modern Prima Luna tube preamp. There is the Transcendent Grounded Grid Preamp or the Foreplay preamp to build. Many other good Tube Preamps exist that offer multiple CD, AUX, TAPE, VIDEO and dubbing capability. Optionally a "Phono" section for those who still enjoy the wonders of Analog based sound will add excitement to the enjoyment of your aging LP collection. If you can spin the Cash, buy a Marantz 7 Preamp. These are amazingly versatile and have every imaginable feature you would want. And they do sound killer ! One word of advice, they are expensive to restore and take a skilled tech to do a good job.

About AC Power Cord replacement (and this also goes for old tools, radios, etc.) **

We live among the old and the new.

Fifty years ago, companies never imagined in their wildest imagined future that old tube equipment would still be around and working.

Not because they built these oldies to last 50+ years but because there are people like us who fix and restore them.

I recently received a nice e-mail asking me about my Fourth Commandment of vintage audio restoration.

This person inquired as to "Why?" I recommend that almost every old Power Cord out there over with +35 years of age be changed out for a fresh new one.

What a great question, I love these.......... !

After having personally worked on, restored, fixed, updated, and modified about 45 to 50 vintage original vintage gear from Americana, Japanese and European, I have seen all kinds of safety and performance issues concerning old, factory original power cords. Therefore I will expound on Commandment #4 a bit to clarify exactly why I say it's good practice to replace old and frayed power cords.

Carefully examine the spade ends of the original power cord. Some, not all of these connectors are oxidized and have lost their outer coating. You can try to wipe them with some steel-wool and see if they are still firmly fixed into the original molded plastic end. Inside the molded plastic lay the actual contact and transition from the Spade to the Wire. This one cannot see as it requires breaking open the molding and ruining the cord. I have done this on replacement cords and have found some interesting things. The electrical connection between the spade and the wire was on some cords, oxidized. In other's it was clearly intermittent and in the worst offenders the rubber had reacted with the metal and caused it to change color, sometimes I saw  sickly moldy green to a brownish substance that looked like ground cinnamon. Some of these internal connections are mechanical and the rubber makes the contact resistive. Others, the connection is soldered and the joint has aged in a non-graceful manner with the rubber, solder and wire all reacting in a non-graceful manner.

Next off, I would carefully examine how "pliable" or "supple" the original rubber cord is. You should bend the cord and look for broken striated lines, these indicate that the rubber has chemically changed and has not maintained it's original insulating properties. You may actually be able to see the wire core through the cracks as you bend the cord; REPLACE.

Sometimes, after 48+ years of sitting around in all kinds of weather, from the Humid to the Salty Air, to the ideal Arizona dry, the wire inside the power cord becomes reactive with the rubber that encapsulates the wire and causes all kinds of problems. One such problem is an increase in the series resistance of the wire. The extra series resistance can be on the order of a few distributed ohms to up to 5 Ohms. This will cause the wire to limit the current delivery to the power transformer. Also the wire will probably feel warm to the touch after 1 hour of play as it dissipates power and affects the instantaneous current delivery to the primary of the power transformer. Some power cords are 'classic' examples of bad behavior. One such case are the see-through Golden Lamp cord. These cords are notorious for going resistive, turning green and affecting fluorescent lamps; REPLACE.

Finally, the wire gauge of original power cords is typically on the order of "AWG 18 to AWG20."

When one replaces an old power cord, the wire gauge can be increased somewhat and it can improve the performance of the amplifier or component. You can experiment by using "AWG 16" up to "AWG 10", quite an exaggeration I believe.

When in doubt "AWG 14" works wonders and "AWG12" is about the thickest you want to go, unless you have the extra space on the internal lugs in the amp for this thick stranded wire.

What works well for me is "Super-Service" Power Cable CAROL 14/2 for Larger Tube Amps and 16/2 for Preamps, with a nice new Plug at the end. If you choose to use a 14/3 or 16/3 with the safety ground, be aware that this extra wire on vintage non-3-wire power cord models may, or may not cause hum. Experimentation is in order. The extra 3rd wire is a fantastic way to eliminate chassis shocks, but most Vintage amps have the Chassis ground and DC ground common. If the DC ground is not a single point ground, but distributed, this can cause a ground loop. Also the connected components can interact with this safety ground and cause hum even when the amp does not hum with nothing connected except speakers and power.

If you feel that the original power cord is a must, then carefully inspect it and clean the spades. Make sure that it is not worn, frayed or warm when in use.

Your local Fire Department will thank you, and you will make U.L. proud !

A good tube amp will require that you set apart at least $800 to $1000 or more when buying a worthwhile already restored or to be restored Vintage tube amp. Budget a minimum of $1250 for a brand new tube amp and about $500 for a regular vintage tube amp in un-restored condition. Then add another $300 in parts to fix. Premium branded vintage amps such as Marantz and McIntosh fetch prices much much higher today than they did 10 years ago. Yet these amps may not be the best investment for a particular person depending on the condition of the equipment. I would dabble first with a simple amp, and if I like what I hear, then the expensive stuff can come as a reward for patience and dedication.

If you feel that you must own older 'Vintage' tube amplifiers for any specific reason; the looks, some nostalgia, the pride, the smell, some particular sound or memory of sound, a conversation piece for guests, or even an antique  shelf 'dust gatherer',  be prepared to spend time and money for proper restoration. If you don't it's only a matter of time before the power tubes fail, some capacitor explodes or resistors smoke and fry. 

There are no shortcuts in restoration work, you either restore or you don't. There are professional restorers, and if you should have such a budget to pay the premium price, please give the "Doc Fisher" a call. He does some absolutely stunning work on bringing Fisher amps back to glory and the cosmetics results are stunning, something I lack in my restoration efforts.

Believe me it's risky business to use, on a regular basis, any un restored Vintage tube amp in original condition. Even if the amp was sitting inside it's original box in 50% humidity since 1959, internal components will age and eventually fail, often taking out with them power and output transformers.

Should you plan to do all the repair work yourself, or are just learning about vintage amps and electronics, be prepared for many moons of frustrating tinkering, plenty of hum, crackling noises, and distortion. If you are non-technical and cannot solder, get help. Be careful, tube amps carry lethal voltages that can cause death. In the hands of the in-experienced, 'Live at the Pearly Gates' may be the title of your next CD. 

Furthermore if you don't own or avail of a tube tester, you will be going blind into vintage tube audio, or at least be at a severe disadvantage. A tube tester for Vintage Audio is like a Hammer for a carpenter or a scalpel for a surgeon.

You may call me a pessimist. I see myself as a realist. 

I am mentioning these things here only as a first reality check. You decide where your bounds and risk levels are. 

One common mistake for tube newbie's is the urge to 'play around' and roll-tubes. Watch out! replacing working tubes with one's of 'unknown origin' is a recipe for disaster.  

Not all new production tubes arrive in working condition, there will be duds, just like there are dud transistors unless they are sold tested and with a warranty. 

Some current production and 'tested' NOS tubes I have received are totally DOA, despite the fresh new box they came in or claims from the Ebay seller as tested and guaranteed. 

The warranty is what saves me every time this occurs. I have had bad luck with Parts Express and MCM. They sell far too many things to be able to deal with finicky tubes. Almost 40% of my orders from these mega places result in some duds.

Also be wary of tube vendors not offering tested and matched tubes. Buy tubes only from reputable dealers that are pre-tested. Some Ebay tube sellers are fantastic, yet others are re-labeling Chinese tubes as Telefunkens, Amperex and some Made in Germany tubes that were never made in Germany. Some are even selling Amperex 6550 made in Germany! Amperex never made a 6550, and none of these were German made. But sometimes they are good re-labeled Chinese or Russian tubes that work well, if the price is reasonable.

Once you complete your restoration, you add-up all of the parts receipts and compare this to the total price of let's say Audio Electronic Supply's "Super-Amp". Or get a pdf copy of Audio Reality and build a pair of SX150 Mono-blocks and get the whole thing over with. I doubt that you will need more power unless your music room is large or your hearing is shot.

One could purchase a new "Super-Amp" and be choosing CD's instead of a new Weller and a $300 dollar parts order to upgrade a $400 dollar Ebay amp. 

I may sound a bit over 'pragmatic', but personally, this same situation happened to me. I am telling you here so maybe you can choose to avoid frustrations the first time around. My first Ebay Vintage amp was an A500 Model from Harman Kardon. This amp gave me a few white hairs. It took me nearly 4 months of almost daily efforts to get the darn amp to play without buzzing. Eventually this amp developing a new problem with some Chinese Oil caps that were shorting. These things seem to be alive after awhile. The buzz ended up to be a $2.00 SPST slide switch, not the $100 in parts I replaced.

Funny that after I ended up replacing many parts, it was the $2 dollar slide switch that was causing the A500 to hum on Channel B. A little Cailube on this switch and the problem went away. Yet in the process, I re-built the power supply and most of the basics were re-newed. I made out in the end with a more reliable amplifier but only after about $380 additional dollars in parts for a whopping $700 dollar investment in a piece that is as ugly as they come, yet sounds heavenly.

Another newcomer is being sold by Upscale Audio, these amps promise to be a good value for the money. They are branded Prima Luna and look as good as anything new out there. Sturdy and well built seems to be my first impressions from looking at the photos, positive reviews also help....

Be wary of angry Audio Forums especially Here lurks a species of sub-human who thrive on anger and anything obscene. Aggressive 'know-it-all' cohorts who gang-up and create amazingly long threads bashing each other. One surf into "" and there is a constant cast of characters unlike anything the tube audio hobby ever imagined. These guys communicate in four letter word, regional slang and coded messages. It's been now a few years when these guys shouted me off. I haven't returned to that news group since. And to be honest, I am not missing anything worthwhile.

Smart-alecks are a dime a dozen. Yet one thing is for certain, theses guys may not lead one to a properly restored amp or give the advice you need.

Many of these 'cheapskates' would never actually pay for a Web site, much less offer one free help with give away scanned schematic or an extra 0.65 Postage Stamp in the mail.

Heck, some of these people believe that tube amps are not expensive, that re-winding transformers is an economical alternative, and talk of the 'fantastic sounding' amps they built from scrap parts for only $50 bucks.  Some guy claims that he can scratch build a pair of Carver Silver 7's for less than $1500.00

It's also amazing how misleading people can be and also how much damage a keyboard and some forum space can be for a wonderful hobby such as Vintage Audio restoration.

The safest and best way to enjoy tubes in the new millennium is via a fresh NEW tube amp. Follow the instructions, fill out the warranty card, plug & play!

There is a deeper and broader side to this hobby that goes right over people's heads, that's why people buy TIMEX clocks, $6000 Low-Ohmic breaker panels and other gizmos that blur the border between reality and fantasy. To state that a Dynaco PAS3 can be 'significantly' improved by yanking out everything, you end up with a Dynaco PAS3 case with lots of expensive boards. I would buy a new tube-preamp instead of doing this to a old Dynaco, unless of course the condition of the preamp merits such alterations. 

Yes, small mod's can improve reliability, but altering the complete package defeats the purpose of restoring yester years technology. You lose the original intent of the designer and end up with a totally different product. Not that this is a bad thing, but the purpose of Vintage restoration is to preserve, not alter.

A NEW tube amp eliminates 90% of problems, leaving only a choice of speakers, cables and sources to deal with.  Simple acoustic room treatments, nice area rugs and some speaker placement work makes up the last 10%.  Some people don't realize how much time, money and effort it takes to bring an old tube amp back to top form. As far as the most important aspect are room acoustic treatments. Pay special attention and read, read and read good books on this topic. Room acoustic are just as important as the equipment if not equally so.

Believe me, there is no magical formula for tube sound, it's all in the design and execution of the product. If you build a perfectly optimized design with normal off the shelf parts the results should be satisfactory. Now, if you go ahead and spend hundreds of dollars on fancy resistors and capacitors from the start, you never gave the design a chance to show it's true colors. I would fix a Vintage amp with standard caps and build up to the exotic parts down the road.

Now taking a factory assembled tube amp and brute-force changing out of parts and components for the fancy types will be only as good as the work of the technician replacing the parts. Unfortunately there are many people out there who claim to be technicians and tack-solder leads into clipped tags without even a mechanically secure crimp or bend. You then end up with a $3000 amp that was re-assembled by an incompetent technician. A perfectly good amplifier meets Joe the soldering whiz. Clip, clip and replace with fancy resistors and expensive capacitors. Another risky proposition akin to a tossed salad approach to 'upgrading' sound that never needed upgrading. 

Once again a NEW amp over a Vintage amp is almost always a better first choice, regardless of price and condition.

Initially leave behind notions that expensive capacitors, Teflon-Silver hookup wire and exotic resistors always elevate the performance of old amps to heavenly levels. 

Let's get real... this type of tweaking, if it helps at all, comes way later in your future. Focus on the basics as 95% of the music is to be found there, the rest is part by part experimentation. 

Our recommendation is to start off NEW, and then learn to own and cherish the 'Vintage' stuff. 

In my 10 years of playing around with old amps I have had them quit in the middle of a jam packed music session, create some pretty strange odors, and exist with noisy controls that may never ever go completely noise free. 

Be aware that some, but not all vintage amps can run HOT when plugged into today's 123 VAC line voltages. This is mostly due to the un-regulated nature of their vintage tube power supplies. Often, if one does not have a means to control the line voltage towards the amps power transformer primary, tubes can wear out 25-30% faster. 

Devices such as Variacs, power supply modification or bucking transformer modifications compensate for 'boosted' B+ and filament voltages. Once again, not all vintage amps exhibit this phenomenon. But when they do, it's really easy to detect. With a DC voltmeter set to the 1000 Volts range, compare the voltage values along the Power Supply chain to those shown on the original schematic. If more than 10% over, trouble is right around the corner.

Nowhere is this more true that with DIY tube amps. Power Supply design and implementation is part science and part art, unless you can build and graph the power supply regulation curve to predict where the voltages stand when loaded at different current levels. If you have a bench HV Tube Power Supply, you can easily build your amp, power the amp with the variable power supply and work backwards to determine what power transformer best suits your design.

Never use a 400 ma capable plate transformer to power a 150 ma amplifier, you will literally cook the amp. Something similar goes for the filaments. If you exceed the filament voltages by more than 10% you risk burning out the tubes early. In addition boosted filament voltages are a source of noise as the electrons are expelled at a greater rate than necessary and the resulting electron cloud is too much for the required level of currents. One sure sign that you are cooking your tubes is the crackling, glass like sounds they may make when warming-up. I have wasted many an EL34 quad with on a boosted DIY Mullard amp. With tubes the higher you go in voltage the more complex the amplifier becomes.

Some manufacturers claim a very broad regulation capability from 115 to 125 VAC on an amplifier's specification, this is mostly un-true. Dare to run any tube amp on 125 VAC and look at the plates of the power tubes. You may not like what you see. 

There are amps that can compensate better than other as they have very good power transformers. But others simply cause the whole DC voltage distribution to boost above the 'red-zone.' This is yet another vintage amp caveat to consider. 

Variacs can take care of this instantly, but you need to buy a quality Variac, not the one's sold for $99 on Express Parts Sites. 

Another less optimal approach is to modify the power supply. To achieve correct voltage distribution on the original schematic when connected to a regular 120 to 123 VAC mains you will need to introduce an additional voltage drop in the power supply. This entails and extra cap and resistor. There is also a method where one can take a choke and install this in the primary of the mains transformer. This is called a 'bucking' configuration. Leave this one up to the experts as the there are several complex variables to consider when introducing such a device into a transformer's primary.

Vintage amps are almost always cranky devices that require special care and constant attention. Let it be known, if you can't stand minuscule yet perceptible hissing on your tweeters, slight but perceptible low frequency vibrations on the the woofers, and other such vintage 'idiosyncrasies'; forget about vintage tube amps for now. Buy a brand new modern tube amp and get on with the groove. 

As with LP's one has to be willing to hear through vintage imperfections. It may be near impossible to eliminate low level hum and other such vintage malaise, it just comes with the territory from an age where technology was younger.

Clinically 'perfect' tube sound may only come from equipment that is properly set-up, calibrated and re-tubed with some pretty expensive stuff.

Many designers today have elevated the performance of tube amps by implementing pretty slick designs using the latest state of the art components and new ideas. It may be that feeding preamp tubes with AC on the filaments is no longer an acceptable thing even for power amps. There are new topologies that offer better sound that was not the case 30 years ago. Output transformerless amps have come of age, and the speakers needed to match these amps are also available, but they are not cheap.

Today's special high power MOSFETS, Solid State devices and Fast Switching rectifiers provide far better reliability than they did 30+ years ago. Selenium is now a thing of the past. You can still find this kind of rectifier, but I would substitute for modern Silicon devices.

In fact, I find it really interesting that more designers aren't implementing regulated High Voltage power supplies in modern tube amps on a regular basis. I would believe that a regulated power high voltage power supply will improve performance.

The more you get into this hobby, the more you realize what really happens on Ebay and other audio trading sites. As the nostalgic and sonic merits of Vintage tube audio devices spreads, I can almost envision a future where the prices we pay today for these pieces of junk will be peanuts compared to what the same junk will sell for.

I have witnessed how the lowly Dynaco ST-70 amplifier would hardly fetch $100 dollars on Ebay. Now you can't approach a butchered example for less than $350 dollars. My suspicion is that, people like me have created a wave for others to buy specific models of old equipment after reading a magazines article and word spreading. One article in Listener magazine on the Dynaco ST-70 created such a wave that still permeated Ebay today. Darn I should have bought a ST-70 when they were going for $100 bucks!

My final advice: Start new and end old. This way you acquire experience and have music during the good and the bad times.

I have experienced first hand that some NEW production tubes cannot sonically compare to NOS tubes, yet in some areas of performance, New tubes shine. 

The fact is that some Russian and Yugo tubes can literally blow a NOS tube out of the water! Yet no manufacturer has ever come close to duplicating a real KT-77 (or even tried?)

For one, the purity, availability and quality of materials required to manufacture tubes are much harder to source today than +40 years ago, and it's also much more expensive. 

Some new production tubes can handle more abuse than their equivalent NOS substitutes, but sometimes it's the other way around. 

Yes, technology has improved, but we are running out of the availability for the pure elements necessary for tube construction. Try to buy 10 kilos of pure Rhodium, you need to take a trip to Africa.  Have you ever seen any Black Plate Russian tubes anywhere?

Another fact is that NEW amps may not be designed to readily accept NOS tube substitutes. 

And the other way around, some Vintage amps refuse to work with new production tubes. 

Believe me..., it's all a bit mystifying but palpably real. 

Just because it's the same tube type don't mean it will perform well in every amp. 

There are also some MAJOR mistakes people make in using tube substitution manuals. Some of these manuals have GROSS errors and can cause one to damage an amplifier. One case in point that I know of;

Tube Substitution Book by "SAMS Publishing" - shows EF86 as a 'drop-in' substitute for an 'EL-84', WRONG

I wrote to the author and so far I am waiting for the next edition to see if it was corrected.

Some Amplifiers require 'tube matching' and 'vendor specific' replacements with special numbering systems. Mesa Boogie is one type amp that Mesa recommends only Mesa certified and tested tubes. The other one that comes to mind is 'Affordable Valve Company.' 

Amplifiers that are designed with output stages using 'fixed bias' will requires far better valve matching than those designed and built with 'Cathode Bias.' So be for-warned when replacing power tubes with one's that have not been professionally matched. Matching power tubes on a Mutual Conductance type tube tester for equal reading is also meaningless. Tube matching requires far more test equipment than a simple 0 to 130 % tube tester.

Some amps are more forgiving to variations in tube characteristics than others. 

But some amps will run new tubes into the ground if not properly adjusted (biasing adjustment) or matched (tube matching.) 

Our recommendation; read the instruction manuals, read about tubes and don't play around too much. If it isn't broken please don't fix it.. 

If it's a vintage piece, order a copy of the repro-manual from one of many web sites, A.G. Tannenbaum or the Manual Man. 

Educate yourself and read about your particular component, research on the web, peruse, analyze, inquire.... etc.

Just don't believe everything that some well meaning forum person suggests. Always verify first with a reputable source.

Vintage Tube audio is for people who become involved with their equipment, it's not a 'plug and play' scene.

Modern replacement tubes are a great way to keep a piece of equipment working properly. Just be aware that some vintage amplifiers were designed with very specific operating points that often will not result in the best sound with modern production tubes. So a bit of tweaking may be required. Some vintage designers used 'highish' grid resistors that don't work well with some current production tubes. You can lower the value of these Grid resistors if you compensate and make the signal capacitor value higher. This keeps the time constant the same and also the magnitude of the frequency pole.

Yet, I have to mention some rare tubes that are and were out of production for several decades and now are available once again, except for one such type, the 7355.

7355; This is the rarest US Audio tube of them all. If you have a Harman Kardon A500/A50K, buy up all the 7355's that you can as this is one tube that is bound to go the way of the Dodo Bird. Sweet in the mids and having extended high frequency capability, the 7355 is not the best tube for extended bass, yet creates that vintage 'curtain-of-sound' effect some people prefer for New Age and Light Jazz Music. Gone forever but not forgotten, maybe this one will never be copied. You can have the amp re-wired to accept other tubes, but there also needs to be a circuit modification as this is not drop-in compatible with any other tube. You can use a Sovtek 7591XYZ in place of a 7355 if you carefully modify the amp. Surprisingly the 7355 is more of a compact 6L6, 6L6GC, 5881 and KT66. The Sovtek 7591XYZ pin's out almost identically, except for one of the pin's on a typical 7355 socket. You can completely re-wire the A500 sockets for the 6L6 family of tubes or buy the 7591XYZ and follow the instructions I made on the Harman Kardon A500 tube amp section of this web site. The 7355 is the 7591 version of the 6L6, compact and able to allow designers to make the physical size of the equipment smaller.

7591-EH; The american version of this audio tube was designed to squeeze the maximum amount of music from the smallest practical size. Out of production since the mid 80's the 7591 was not a rare tube until people hoarded them in the 1980's. Recently the 7591 is available once again in two modern replacement versions. Electro Harmonix, the U.S. importer of Russian made EH tubes offers the 7591EH. This 7591EH is a re-designed 5881/6l6GC tube with a 7591 electrical specification. The size is much larger than NOS 7591 so it may not fit in every vintage amp. Check the size before ordering. The sound is much different than NOS 7591's, yet I like what I hear, even if words cannot describe the difference. This tube appears to tolerate Vintage Amps better than the 7591S sold by JJ. The 7591S JJ tube has garnered a very poor reputation. I would venture to say that they have not managed to solve the manufacturing challenges required to make a real 7591 tube in the original size. This is more of a mechanical issue as the physical tolerances required make the 7591 an labor intensive and expensive tube to reverse engineer. Svetlana gave up and decided against this. Even vintage 7591 and 7591A tubes suffered from production problems. This is one small sweet sounding power tube I love to listen to. It has a magical sound in Push Pull configurations.

7591-S; JJ electronic in the Slovak Republic has recently released another version of the 7591 in a size very similar to a NOS 6V6 tube, and almost an exact physical match to the original FAT base 7591 NOS tubes of the 60's and early 70's. Later on the 7591 came with a smaller plastic base known as a Coin Base (Sylvania, RCA, GE) but mostly manufactured by one US company and re-branded at will. Well I ordered a matched-quad of these 7591S tubes. Unfortunately the tubes run hot in my Harman Kardon A700 amplifier. I suggest that anyone using these tubes ask for 'cold' quads. Why you may ask? I learned that some tubes will draw more current at the same conditions when others draw significantly less current. Some Vintage amps have no provision for adjusting the bias level, as in my Harman Kardon A700. Installing the quad of JJ 7591S was a dismal failure. I suspect that somehow these tubes don't quite duplicate the original 7591's. There is no mystery here. Just look at what people are charging for brand-new NOS 7591's, $400 per quad. The reason is simple, real 7591's work better than new production. I ran some tests on these 7591S and compared the results for real 7591A and 6GM5 tubes. The circuit I made strapped them in triode mode with a 100 Ohm resistor between G2 and the Plate. The results indicate clearly that the 7591S tubes draw between 4 to 8 Milliamps more current than real 7591's and the 6GM5's. Sonically they are a disappointment. Time to scarf more 6GM5's. I use the 6GM5 to 7591A adapters sold by Antique Electronic Supply that are no longer available.

7868-EH; Long out of production US Audio Tube, the 7868 was the rarest NOS power tube of them all, now second only to the 7355 power tube that is most definitely out of production with NO substitute except a 6L6 re-wire or a 7591XYZ with careful attention to what is on Pin #4. The 7868 looks like a 12AX7 on steroids. Now that Electro Harmonix released the 7868 again, many a closet amp can once again sound without having to order $40 to $80 dollar a piece NOS examples. And now you can have the luxury of having matched Duets and Quads, unheard of with NOS 7868. Electrically the 7591, 7868 and 6GM5 are almost identical, except for one small inter-electrode capacitance parameter. If you re-wire the bases, you can drop-in any of these three tubes and expect the circuit to operate properly. The problem is that each tube type has a completely different basing.

2A3; This Directly Heated Single Plate triode tube is once again available via Sovtek and Shuguang. It will not sound 'right' at the typical 250 Volts, 60 Milliampere bias point for the venerable 2A3. But in the proper circuit, this tube works magic. Alesa Vaic also makes an expensive example that promises excellent results. The 2A3 tube is often referred to as the 'most correct' sounding audio valve. Neutral as hell and sweet as pure cane sugar. Midrange magic and highs to tame a Lion. With the light's out and a Diana Krall song, you a bound to get lucky very fast !!!

300B; An amazing directly heated filamentary triode that is once again being manufactured in Kansas City, MO by Western Electric. Some Triode Zombies claim say the 2A3 sounds better. Yet, in the right circuit, the 300B delivers Single Ended heaven. Sovtek, Alesa Vaic, Shuguang and others are also making their own versions. Nice tube, historic and musical

Where do we shop for great tubes. Here are some useful links so you can search for the tube you are looking for. I have ordered tubes from every one of these vendors and they are A#1

Jim McShane

Upscale Audio

You cannot go wrong with any of these tube dealers. I have ordered from all of them with 110% satisfaction money back guarantee, and only one tube ever (6CW4 Nuvistor) was DOA and promptly replaced. 

One last word here, please make sure that you don't install new tubes in an un-tested amplifier. This is the most direct way to damage a perfectly good vacuum tube and maybe the amplifier output transformer.

Despite what people say, tube rolling is a risky art that one needs to learn. Many an amp or preamp have suffered during a tube rolling session, especially when swapping tube rectifiers.

It's also not a good idea to constantly roll tubes, it put unnecessary stress on the pins and the glass. If it sounds good, please, sit down and listen to music, leave the amp alone.

Of Tubes, Wine and Humans

Listening to old tube equipment is like sampling Wine, each type has it's own flavor. Yet, the majority of people who I talk to about this tube hobby all conclude that they are not able to hear any difference between ANY sound system. So they ridicule us music lovers and question 'what is all the fuss about.'

Others claim that onle New Old Stock tubes sound good, and that current production tubes are blah. Yes we do have a religious overtone here. Belief is a sure way to confuse the facts and spoil the hobby.

I always find Music and Electrical Engineering difficult to put in laymen terms, therefore I often use Food and Drink to describe things, it allows me one sense (taste) to be compared to the other sense (hearing), that's just my wacky style. 

Test #1:

"If blindfolded, could you tell the difference between a Cabernet Wine or Boone's Farm Strawberry Hill" 

Amazing, most say they trust their palate, of course I can taste a Cabernet and know for sure. But, same person, asked:

Test #2:

"If blindfolded, could you tell the difference between a Mini Component Shelf system and a Vintage Tube amp"

Huuummm, they say.... now that's real difficult. A flat out refusal to trust one's hearing acuity over one's taste buds. I get the picture, and it's almost always a cynical one with a smirk.

"Only dogs can hear those frequencies"

"I cannot hear the difference"

"My ears cannot hear a difference"

"I don't have that type of hearing ability"

If we talk about a single tone, amplified over a stereo system, of course our ears will cut-out at about 17.5Khz. Some people can actually hear 18 KHz and a bit higher. This is exactly NOT the point. I don't sit down and tone-out my equipment, unless it's on the test bench. 

I use electronics to reproduce music, not to see where it cut's-out and how high or low the amplifier can go, unless testing the component.

Yet 99.9% of CD's, LP's Reels and Cassettes contain musical energy, not test tones. Yes there are some frequencies that are higher (we mostly do not hear them) and lower (most stereo systems cannot go cleanly below 30 Hz overall) and feel them, yet the fact is that most recordings do not contain significant amounts of musical energy below 30 Hz or above 18.7 KHz anyhow.

The real action occurs right in between the 45 Hz to 16 KHz range and specifically in the 1.5 KHz to 10 Khz range. This is where the amplifier should be it's most linear, and the speaker system able to amplify this energy for our enjoyment. There is some virtue to designs that are linear to 100 KHz, yet the higher you make the amp's bandwidth, the more difficult it is to stabilize the design. Of course very deep bass is a challenge for any amplifier except the most exotic, but most recordings don't have any, so what's the point ?

What matters is what is happening right in between the 'prime' frequencies and our ears and brain.

If you are lucky to audition a finely-tuned Single-Ended Tube system with some excellent recordings, I can almost guarantee that amazement will NOT elude you, you will hear a MAJOR difference in the musical presentation. Single ended may not be technically correct, but music it sure delivers. No extreme low bass or extended high's. Yet what reaches your brain is very nice music indeed.

Now whether you like what you hear or not is the subjective end of music appreciation, I prefer to stay away from that discussion. Unless you serve me some Scotch and Sodas first to loosen my tongue and distort my judgement. 

This is the grey area we cannot just ignore. Some people can hear a finely tuned stereo system and dislike the sound; oh well, so what.

My conclusion, if you like the sound great, if you don't ... great again. You go your way, I go mine, end of story.

My recommendation then is to buy the simplest system you can and be happy. I am not worried, concerned or even bothered by this. Some people don't have music as a hobby and a stereo for them is like a kitchen sink, it works and I use it when I need it.

But, what can get under my skin is the return comments from people that 'doubt' that systems can out-perform basic setups by 200%, when in fact they really do. This debate goes nowhere, yet we still love tubes and the people who curiously inquire about them.

Music loving people enjoy and cherish the emotion, feeling and presence of a good Hi-Fi system, doesn't matter whether it's tube or solid state. Tubes don't sound any better than transistors, we cannot generalize. Yes, Tubes are easier to design with and require simpler circuitry. 

Hence the music enters and leaves a more 'direct' path without acquiring any extras along the way. 

There is also a false notion that tubes distort and transistors do not, also wrong. If any amplifier is properly designed, is will sound excellent.

All amplifiers distort, tube or solid state, it's in their nature. Yet given a proper design, setup and installation, any distortion should then be at acceptably lower levels. One really does not need 0.001% THD. Another very grey area where some claim that the harmonic structure of the distortion makes tube distortion more palatable than transistor distortion which can often make music sound dry and brittle, you be the judge.

I also find a synergy between people who enjoy fine music and own good stereo equipment. I prefer tube amps because I can build them at home, end of story.  

Solid State amps are much more tedious to home-brew and harder to design, my opinion. 

Some of the most tedious courses in College at Florida Tech were Analog Multi-Stage Solid State amplifier design. If you understand all of the steps required to complete a working Transistor amp, you would probably pick-up a copy of Tube CAD and stay away from Solid State. Low, Mid and High frequency analysis with so many different formulas to memorize, ugghhh...!

I have read that solid state devices require electrolytic type capacitors in the audio signal chain. This causes non-linearity's and introduce additional distortion. Interesting....

Yet those pesky PC boards that burn, the Etching Chemicals, several Heat-Sinks, those special Transistors, very narrow biasing ranges, Thermal Stability for Operating Point and Amplification Factor; wow... there's a lot to think about with Solid State.

Transistor amps require far more components, special construction techniques, regulated DC power supplies. 

All of this makes solid state home brewing tedious and probably more expensive in the end.

I find it way simpler to drill a chassis, punch some holes and screw down transformers. I go to Radio Shack for some tag-boards and fuse holders, plus some nice gold RCA's.

Go ahead and order custom PC boards for your project, unless you have a buddy who can make them, these may cost about the same as a nice set of output transformers. 

What would you choose then 2 ounces of Fiberglass and thin metal foil or +6 pounds of iron and wire, wound to perfection.

My slant is not in any way of form a standard, it's just how I have approached this hobby. I chose to become a home-brewer, not that I believe myself to be a source of absolute truth. I lay it on the line and let you decide. 

Some people collect

Some constantly trade

Some stick to one system for 10 years.... 

We are all probably loving the music, no-one is wrong we are all either 100% correct, or close.

It's about having a good time.

Now read this fantastic forum posting. I copied it verbatim here for your enjoyment. This 'test' shows that expectations, our brain and some plain-ole trickery can make anyone hear a difference. 

I guess when we expect to hear a difference; darn-it... maybe we will !!

"I do a bit of guitar amp tweaking and repair here in new york, mostly for friends. A friend of mine, who is a very intelligent guy (although he religiously reads "Guitar Player";)), asked me one day to change all of the caps in his Deluxe Reverb reissue to paper-in-oils, and select resistors to carbon comps. I said sure, and gave him a price. The next day I called him and said to come over and listen to the results. Of course I hadn't so much as loosened a bolt on the thing. He played for a minute or so, and was EXSTATIC. It's so much more "responsive" he said, more "fluid and dynamic". He couldn't believe the difference. I finally told him that nothing had changed, and asked if he still wanted me to do the work? Guess what - he said yes!:confused: He did not accept the reality of the situation, even when presented with the facts. My trick had not taught him anything, but it taught me a very important lesson - the brain can make the ears and the eyes see and hear things that simply aren't there. I don't think you need an engineering degree to understand that. There are dozens of other stories, especially from the dawn of the stereo age, listening tests, etc, that one could bring up, but as I said, neither side will be convinced so let it go."


In my musical experience real musical 'scale' comes only with proper speaker size and amplifier power. It happens when I attend a live Symphony, or any live concerts. 

Scale also happens when loudspeaker size and efficiency are carefully mated. Yet this means more power, more space and much more money.

There are $10,000.00 speakers with over +101 dB efficiencies that are very tube (not wallet) friendly. Zu Cable makes the Definition, a quality Full range product to satisfy 95% of the musical needs of most mortals.

Specs like 'Never below 10 Ohms', phase coherency, book-matched wood veneers, where does it all start and end.

But less than 1% of the people out there would actually pay 10K for a pair of loudspeakers. I would, as long as I heard them.

Yet, the bigger, better full range stereo setup will produce real bass when driving normal rated 'efficiency' full-range speakers and a bigger scale in presenting reproduced music. If you like your music at moderate to loud levels and have a need for feeling the Bass, you need to spend more whether 3 watts from a 2A3 amp of 300 Watts from a behemoth.

Full range speaker systems dig into and bring out the 'most' from recordings, they achieve their full sonic potential. But quality Bass is also a function of the music room itself. 

True, Mini-monitor speakers are small and nice but attend to a specific musical taste and need. Not all people like or agree with Mini-monitor sound. While particularly good at imaging when properly placed in a room, Mini-Monitors are good for shelves, corners and near-field listening. They get lost in larger rooms in terms of sound. Subwoofers are the only way to balance the presentation. But these also have their complications. 

In fact, for places where they can be nicely tucked-away out of the reach of pets and curious rug-rats Mini's and Subs are great.

There are also speaker setup architectures for as Near-field and Far-field monitoring techniques. These two distinct stereo techniques can offer different sound-staging. For those whose musical taste is limited to small-scale ensembles and simple acoustical music, I would say try a near-field setup. Near-field monitoring involves a specific setup where the speakers are brought almost kissing close to a sitting chair and the listener's head is at one corner of a isosceles triangle. This simulates a small acoustic space and often allows the listener the beauty of 3D sound in a small area, not to mention the savings in amplifier power as a few watts is all that is needed for such a setup. I can say it almost sounds like headphones.

Then we are back to power and quality.... I read that Paul Klipsch once uttered these venerable words; 

"What the world needs is a good 5 watt amplifier"

For some music lovers, only Single Ended type 45, 2A3, 300B, 572, 845, and 211 based amplifiers with the proper speakers will 'open-up' the pearly gates and actually bring Stan Getz into your music room. For others the dynamics of Push pull designs are a must.

It's the immediacy of female vocals on SE equipment, the timbre of a trumpet and the sweetness of a flute that are conveyed in a manner unlike any typical tube audio system, I say Single Ended amplification is in a class all by itself. I understand that this craze all began in Japan and has spread to the R.O.W.. Nothing sounds like pure Class-A amplification. Vocals and piano attain a 'real' state of velvety pureness hard to explain in words.

This brings me to come up with a theory called 'Reproduced Music Presentation Scaling.' This is a concept which I plan to develop into a formal theory some day.

To me 'RMPS' is something about matching a given stereo system to a particular listener in several dimensions, like a dating service. Parameters such as Power, Size, Frequency Range, Tone, Dynamics and Price are carefully matched on a one-on-one personal basis. 

More on RMPS later.....

Another breed of musical enthusiasts are those who is continuously seek 'Holy-Grail' music at home. Continuously trading and bartering equipment, these audio 'speedsters' will never have a given stereo setup for more than 1 month or even 2 weeks. These enthusiasts have some real stories to tell. Having them as friends allows one to sample some pretty exotic equipment in the bartering process. They are constantly 'swapping-out' stereo equipment in a manner not unlike the name of their main watering hole... 

If you want to take a great tour and check out a really nice array of different pieces of audio equipment, this is the web site to visit! 

At Audiogon an amazing amount of different varieties in amps, speakers and accessories can keep you entertained and mesmerized as long as you have a Broadband connection.

If you ever meet these audio speedsters, remember that ANY equipment you may fix, modify, trade or sell with them will inevitably be '-gon' for something else. This can often be sad for people who do 'favors' for a speedsters, only to see precious time and work traded off into oblivion. It's like taking a pet you no longer can care for and not knowing who the new owner is you leave it up for adoption. Often there is no regard or understanding of how much care and workmanship went into restoration. The true nature of the equipment itself is lost. No regard to the sacrifice, time, and history plus the legacy of the amplifier. Even sadder are the people who don't realize the time and effort it took to become a good vintage amp repair person. 

Some precious vintage pieces of equipment may end up in used equipment 'stereo pounds' in need of a good owner. So if you see any such adoption cases, please give them a good home. Some people just don't know what they have, or are able to properly use vintage equipment to realize it's 'full potential' within it's limits.

Also good places to look for old equipment are used audio stores, antique shops and garage sales. Any other place where dusty metal meets Joe-Tube. There just must be still, stashed away in many attics and basements, classic audio gear in great physical condition waiting to be discovered and restored. The current trend on Ebay has brought about a steep interest in vintage amplifiers. The frenzy continues to show complete 'rust-buckets' selling for $100 to $200 dollars when in fact the buyer has no idea of the condition of the transformers.

For the rest of us, the more obscure brands of yesterday offer an excellent entry point into vintage tube audio. The amount of money that people spend for Marantz, McIntosh and Fisher equipment would have pleasantly surprised the original designers.

Some classic vintage designs have been re-issued by the original companies or contracted to a 3rd party. Tubes are alive and well today, maybe more so than 30 years ago.

Keep your eyes open and read for any classic tube gear. This way, you can recognize that one man's trash just may be that special keeper amplifier you saw on Ebay, without the need for bidding.

Maintaining a balanced attitude in such a 'testosterone-laden' hobby creates some real excitement. One's real needs, the size of the music listening area, and a constant comparing this to that, beats a boring weekend at home.  

But Music should be the driving factor for any decision to move on with a better stereo setup at home, not the equipment itself. Focus on buying better CD's and enjoy better sound. Expand your musical tastes by sampling other sounds. Trade off your crummy sounding older CD's for the better sounding modern DDD releases and re-masters. There is lot's you can do to improve your CD collection. I hear AAD and ADD CD's where my original LP's still sound better. I also notice that early CD's are recorded at a much lower volume level that the new all digital CD's.

Plan, invest, setup and enjoy. Maybe 8 to 10 years down the road you will sell that system and move on to some other setup. Your musical tastes then may include live recorded music, or larger ensembles. Eventually I may design a hybrid amp that delivers massive high current Bass and soft velvety tube textures. But in the meantime, just focus on and build up your musical library. 

Shop for CD's, DVD's, LP's, Reel's, etc.. Attend live shows and support your local Symphony or Jazz club. Yes MP3 may provide a short-cut, but on a high definition stereo, it just sounds lacking and dry.

Music is where the money should primarily go, not equipment. And if you are so lucky as to live near real good FM radio stations, a Magnum Dynalab Tuner will open-up your senses like no other component can. Digital cable TV systems offer 50+ channels of nice and varied music. This is a good opportunity to tune-in and sample some other music. 

Write down the artists you like, then seek out their CD's and experiment, grow your collection.

As we enter the dawn of SACD and Super-Multi-Channel formats such as AC3, Dolby 6.1 and 7.1 the P.O.S. = Plain Ole Stereo system may no longer meet your needs.  If so, then focus on a quality Multi-Channel receiver from Denon, Harman Kardon, Onkyo or Parasound. 

Should your preference be for Movies and Home Theater type systems, there are tube based solutions, but they are not within normal people's budgets so I will not even go there!

Any hobby brings a certain charm when approached with simplicity and simplification. Often less is better can produce very nice results. Tube Audio is best when you spend the time to optimize your resources and your mind. Tube Audio should be educational as well as inspirational. 

Coming to terms with simplicity, allowing your ears and senses to capture and recognize good musical sound is key. Recognizing this fact and knowing 'how' to balance musical flavors arriving at the best sound for you is unfortunately not the norm. This is probably what makes people not trust their hearing and remain in denial about such typical "I can't hear the difference statements."

Of course you can hear the difference!, unless you have completely lost your hearing, or have a source that cannot recover the sound properly.

Conclusion..., always treat your ears with care. As I mentioned before, a 20 Watt Stereo System can cause permanent hearing damage. 

In the land of the blind, the one eyed man is king!

Properly setting up, connecting and enjoying a functional vintage 'Tube' Amplifier is never a trivial matter. Endeavoring to repair and restore broken and aged vintage tube amps is the farthest one wants to go in tube amp land. 

Vintage Amp restoration is tedious work and unless one is willing to learn about the past in the future, buy new, buy American!! he,he,he :) 

Enthusiasm is NO substitute for practicality. Repairing any Vintage Tube Amp requires years of skill and specific test equipment. It also requires the knowledge to make things better, not worse. Troubleshooting skills are developed in many different ways. If you have a degree in electrical engineering or technical electronics, you may find engineering types repairing with calculator and paper along with the soldering gun. If you can apply mathematical formulas to a real live tube amp, the knowledge will help in the determination of faulty parts and components. Another method is the empirical way . Technicians rely on experience, visual and test measurements to repair, another creative way to arrive at good sound from Vintage amps. Proper test equipment is the most important troubleshooting aid, and the all important human eye.

Most non-technically inclined people puzzle over the connection side (rear panel) of any 'typical' 50's-70's Production tube amplifier. 

It's not apples to apples anymore. 

When comparing a modern solid state amplifier's rear panel to a vintage tube amp, several questions are bound to arise. Just open up the bottom cover of a Vintage Tube Amp and the looks of 'point-to-point' wiring can intimidate even the most seasoned technician. 

If you have never worked on point-to-point wiring and tube equipment, best leave this up to the one's who do this on a daily basis. Vintage and recent production tube stereo equipment require 'basic' but fundamental knowledge on how things used to be.

I have to agree with other competent technicians that getting into 'Tube Stereo' by buying old fixer upper amps is not a good route. We believe it much better to purchase a brand new tube amp with a warranty. 

Yet if you are good with a soldering gun and have mechanical skills, modern kits can save as much as 35% off the cost of an assembled amplifier, this is one great alternative to save. Yet the savings today are less and less, so it's better to buy assembled.

It's about the reality of things, if you buy a new working product with a warranty, the quality of the sound will be equal to or better than any +40 year old vintage amp at any price, except for a small group of classic designs that still challenge the state of the art today. 

If you are lucky to buy a fully 'restored' vintage tube amp, with a warranty of at least 90 Days, then go ahead. Otherwise look elsewhere. 

Consider that my first real experience with tube amps was attempting to build my own amps from only a Mullard 5-20 book. 

This took me 3 month's to get any music, and it was distorted. My frustration levels only made my learning curve that less palatable. yet today I can readily repair an amp in a reasonable time frame.

In short, depending on where you want to go with a tube stereo setup, speakers are just as important to the sound quality of any tube amp. With characteristically low damping factors, tube amps don't sound good with just any randomly chose speaker. It takes finesse to achieve acceptable sound from a tube amp and a speaker system.

If one is not really critical about this fact, any working speaker system can offer interesting sound from a tube amp, especially the lower powered types, less than 10 watts. Note that I say interesting not great. You cannot expect great Bass from a low powered design, unless the correct speaker system is acquired. Some speakers impedances vary so much that tube amps are not good amplifiers to drive them.

Refer to my speaker section for more details on how to choose a speaker that will work with a tube amp.

This next tutorial hopes to provide the basic guidelines at the most critical point in any Tube Stereo system, the Loudspeaker - Amplifier interface, and proper Mains connections with a quick mains AC voltage level check.

In order to understand Tube Stereo amplification, one must know how to connect and arrange one or more sets of loudspeakers to the amplifier's rear panel. Only experienced eyes can tell from the photos and descriptions linked from Ebay sellers  that most sellers of vintage tube equipment on Ebay have good intentions but no idea of what they are doing when powering-up 40+ year old equipment.

Generally speaking any old piece of tube equipment needs proper care prior to the first power-up after a period of dormancy. Any amplifier not having seen use for many years is not a good candidate for 'plug-and-play'. It's 'best practice' with any amp not to rush for sound. For that matter any power amplifier system in general should be connected after reading the manual or consulting with a knowledgeable resource. 

If you are lucky enough to own a good Variac, powering-up old equipment can be made much simpler and safer. You can build a light-bulb limiter circuit (cheapo way) and still safely test old tube gear. But you also can do some serious damage with a Variac if you don't understand what's going on.

If the piece of tube equipment is diode rectified, you can safely increase the Variac voltage anywhere from 0 Volts upwards to rated voltage which is typical for a soft start with a Variac. Early tube equipment used 110 Volts AC (pre-1940), mid era 115 VAC (late 40's early 1950's) and 117 VAC (mid 50's to present day.) Note that today's 120 to 123 VAC mains voltage can stress some equipment and cause damage. Therefore it's always wise to measure the DC voltage of the power supply system to verify that in fact the amp is not exhibiting boosted DC voltages causing an early burn-out. If it's tube rectified you need to start at least 50% of nominal voltage not to damage the rectifier tube.

It helps to know from a schematic what DC voltages one can expect to measure based on the specified AC input voltage. Also note that most voltages on early tube type sets were measured with VTVM (Voltage Tube Volt Meter) that had impedances much greater than todays digital VOM's so reading will vary a bit, towards the lower side. Today's Digital VOM may only have 10 Meg-Ohm impedances which can causing small reading discrepancies, yet not enough to make a 'real' big difference. Just be aware of this fact when comparing your FLUKE's readings with those measured on VTVM's.

Again the measurement error will tend to be on the low side, reading a bit less voltage than actually present due to meter loading of the circuit under test. When using a variac tube rectified equipment should never be powered-up with less than 50% of line voltage. One may risk damaging rectifier tubes if prolonged low power operation is attempted with any variac. 

Just make sure that you have test speakers or an audio dummy load connected to the output terminals of the amplifier under test. It can be true that a 'No-load' power-up 'may not' harm a tube or transistor amplifier left on for 1 to 5 minutes, just don't walk away for too long. 

Only a selected few vintage designers took no-load operation into consideration and installed either a single load resistor across the main outputs or a loading network in parallel with the output transformer taps. This helps to provide some secondary loading when NO speakers are connected. 

Some vintage tube amps have a provision for Headphone operation. You can safely test these tube amps with some old headphones, just don't power-up with them on your head or risk hearing damage. 

You should use 8 ohm or higher impedance headphones as a speaker substitute. 

Again... please don't wear them upon first power-up, keep the cups safely away from your ears. 

Also, please don't use your precious 'Sennheiser', 'AKG', 'Stax' or 'Grado' headphones for a first amp test!

Most Airline headsets are the best for this purpose if you have an adapter. You want to use throw-away type phones for a first power-up in case that the amp 'motorboats' or has some type of severe hum problem that fries the voice coils.

So once again, remember that very few vintage tube amps have provisions for no-load power on operation.

>Does it work or not?

After one passes the most basic power-on precautions and tests, the next part is to actually try to get some music from the particular amplifier under evaluation.

If the music distorts or has problems on one of the other channel, further troubleshooting is due. If you do get some nice music, then the amp must be evaluated for several minutes to check for any bad smells, red tube plates or some other sign of trouble. The power transformer should not make any audible buzzing noises. In addition to the touch of a finger, one should feel the most minimal vibration or nothing at all.

If the amp has been determined to need servicing, then you must refer the project to a qualified technician or begin the long $hard$ road of fixing it yourself. If you decide to attempt a repair, there will be a significant amount of test equipment that will be required. Rarely one can fix a vintage amp with merely a voltmeter and a soldering iron.

Technical skills take years to develop and perfect. There are many excellent books on the subject of Tube Amp repair, even a video by the late Cesar Diaz should you happen upon a copy of this rare but informative video.

Don't even try to repair any tube amp yourself unless you understand the basics on Voltage, Current, Resistance, Power Supplies and schematics. It's much easier for a technical person to 'cross-over' to tube amp repair. But a non-technical person should best leave this work up to the big dogs.

>Tube amp, no load operation and testing, why you may ask?

The answer is not easy, and maybe there is no definitive answer. But when there is NO loudspeaker load connected to an output transformer device under power and operation, the secondary (speaker side) will reflect, towards the primary (power tube side) an 'infinite' impedance. This in electrical terms is equivalent to an Open Circuit condition, i.e. nothing connected, or infinite impedance. 

No impedance is equivalent to infinite ohms or several hundred-thousand megohms of resistance (equivalent to an electrical open circuit.) Infinite impedance is the term used by Electrical Engineers, open circuit should works for the rest of you out there having read this far into my web pages.

Some amplifiers become may become 'unstable' under no-load operation, and then some just do not. Output tubes may begin to 'self oscillate' causing larger than normal DC currents to flow through the output transformer's primary windings. The net result is heat buildup and a possible output transformer-output tube melt-down condition.

Other things may also ruin your amp such as Bias settings that have been tampered with, bias balance rheostats that are turned completely CW or CCW, making one output tube hot and one not, in effect many things can go wrong. Hey, this is not an easy hobby, but neither is tuning dual SU carbs on an MG. Vintage technology often required larger amounts of user competence and intervention. Things were not as idiot proof in yesteryear. Maybe it's just a reflection of our times. We view technology today as all-problem solving. Products die even before a prototype is built. Today's complex marketing and sales requirements cause engineer's and managers many more headaches.

Yet with Vintage equipment there is never any guarantee.  We at the Music Room recommend as 'safe practice' to always connect a used and not so valuable set of test speakers to any amplifier's under preliminary testing. True, when operating, servicing, testing or taking Ebay photos of the amplifier some may break, some may work and some may not do anything.

Loudspeaker systems exhibit a wide frequency and phase variant load.  This is quantifiable in terms of an 'average' or 'nominal' impedance. When connected to an audio amplifier system any loudspeaker will interact with the amplifier in very specific ways. Some produce excellent sound, while other combinations sound terrible from the start. 

Loudspeakers are rated in Ohms, yet this value refers in Impedance, not just Resistance. The presence of music power is expressed in Watts. And from an amplifier system this value is typically calculated using RMS values of AC voltage. The amplifier 'excites' the speaker elements (drivers and crossovers) and music is made. The air surrounding the speaker is placed into motion in the form of sound waves, and we feel the vibes... cool mon!

Mind you, speakers may be anything from large paper cones, long flat ribbons or even electrostatic types with elements that require special intermediate circuitry to operate. But this is all, in a general sense, what comes into play when we connect speakers to an amplifier and apply music power. (EASY..........., what do you think?) 

Current commercially available loudspeaker systems are offered to consumers in 4 Ohm, 6 Ohm, and 8 Ohm nominal impedances. I say nominal as the value of the speaker's resulting impedance will vary throughout the audible frequency range of 20 Hz to 20 KHz. Almost to, but not almost never a flat curve.  

In laymen terms there are about 3 or 4 types of speaker impedance groups today: 4, 6 and 8 ohms for Home Audio. There also exist 16 and 32 Ohm types being the rarest of them all. Commercial sound systems often provide for 16 and 32 Ohm wiring options and as such, can handle greater power levels with less distortion than consumer speakers, but without the resolving clarity of Hi-Fi types. 

Impedance is not a fixed value that remains the same with varying frequency, unless the impedance load happens to be purely resistive. So the same rules of electronics from Mr. Ohm (here's a link to the man himself.... what a mind he must have had!)

Two sets of 8 Ohm speakers provide a total of 16 Ohms in series and 4 Ohms in parallel. So through Ohms law we learn how to determine the resulting combined impedance when playing around with cables and connections. Either you learn Ohms law or you are not into this hobby. 

Loudspeaker efficiency is another very important specification but not always a de-facto benchmark for tube friendliness. True..., efficient speakers work well with low to medium powered tube equipment while low efficiency speakers require larger amounts of power to operate at their designed center of operation. As a general rule Solid State behemoths often require elephant sized speakers to sound good. 

It is a matter of decibels in this case, where anything below 93 dB SPL (Sound Pressure Level) measured in an anechoic chamber at 1 meter and 1 watt of continuous power is generally not 'tube happy-land' unless the Impedance and Phase plot is such that the impedance represents a predictable and steady load, regardless of the resulting average impedance. It's not good to have a speaker with 16 Ohms if at 350 Hz the impedance drops to 4 Ohms and the phase angle between Voltage and Current happens to be more than 35 degrees. This represents a difficult load for any amplifier expecting 16 Ohms.

The main reason why tube amps don't get along with lower efficiency speakers is that they typically do not have the benefit of high damping factors such as those exhibited by Solid State amps. Tube amps don't deliver the current levels that inefficient speakers demand, unless you have a Carver Silver 7 or a Manley Ichiban.  

Tube amps tend to suffer deleterious sonic effects from Back EMF. A Woofers voice coil returns current spikes back to the amplifier via the speaker cables. And it is the damping factor that determines an amplifier's ability to control this back EMF and thus control the motion of the woofer cone.

Some designers such as Avery Fisher  provided for the 'adjustment' of a tube amplifiers 'damping factor' to overcome the lack of control experienced in the lower frequencies. This was implemented in the form of an extra screw terminal on the rear panel where specific values of damping resistance was connected in order to adjust the output damping factor of the amplifier to better match a given speaker type. 

Back EMF from the woofer voice coil can affect any amplifier and it's ability to 'grab' the cone and control it properly, some reviewers also describe this as 'the ability to wrestle the cone.' The woofer's voice coil sends some back EMF to the amplifier and can cause poor bass response plus all kinds of problems. A proper scientific explanation of back EMF is beyond me at this point, but here is a link where you can read more on Damping Factor and Back EMF from Crown Amplification: damping factor.pdf

Loudspeaker polarity is another important factor to consider. Both speakers must be wired 'in-phase' in order to derive the best soundstage. If the speaker leads are connected in an out-of-phase fashion, the speakers will be operating at 180 degrees out of phase affecting imaging, bass quality and many other things important to high fidelity reproduction.  

So remember, (+) amp to (+) Speaker and (-) amp to (-) speaker for all channels. The best way to be sure that the speakers are in phase is to color-code the speaker cables with some red and black tape to simplify the  correct connection scheme. Test records help to identify this problem but unless the speakers are internally wired incorrectly, the visual method is all that one needs to assure proper phasing. Another visual check is to remove the front covers and power-on the amplifier. If both woofer cones move in the same direction, then the speakers are properly phased. Unfortunately the cones will almost never move when a Tube amp is powered-up so this applies mainly to Solid State amplifiers.

Enough theory, ....lets get practical.

Not so apparent to most folks is that stereo solid state amplifiers have typically (1) dual set of connections on the rear. But in the case of Home Theater amps, there are several internal amplifier modules, each with it's own discrete set of speaker connectors.  This means that one finds Left (red/black) and Right (red/black) terminals only and this may also mean rear channel speakers as well for Home Theater setups. In Vintage Tube audio we concentrate on two main front channels only, leaving the Home Theater setups for future endeavors.

The main difference in between Solid State amps and their tube counterparts (expect for OTL types) is the lack of impedance taps. The exception are some older McIntosh models that used Transistors and Output Transformers for the design. This is not common at all for the audio industry. McIntosh labs was always the innovator, and we are lucky that our Japanese friends kept McIntosh alive.

Most people today when looking at the rear panel of a Vintage Tube amp, scratch their heads. Lack of proper understanding has led to many a fried amp. 

Let's see why....

I always get the same e-mail over and over, HOW DO I HOOK UP MY SPEAKERS TO MY A500 AMPLIFIER ? ... a picture is worth a thousand words:



A total of 5 screws and one jumper wire with a spade end, what's going on here?

The jumper wire is connected internally to the plus (+) terminal (you don't see this connection from the outside of the amplifier. In turn this externally (as shown) connected to the proper impedance tap even before we connect any speakers. The impedance tap selector connection must be properly connected to one of the impedances shown. The loudspeakers are then connected to the (+) and (-) screws independently from the impedance selector screws.

Many a vintage tube amp has seen a catastrophic failure when unsuspecting audio enthusiasts place a short circuit across the transformer secondary when attempting to connect the speakers to a confusing set of screw terminals.

Most new tube amps will still have at least three possible terminal connections per channel. There are Negative (Common), 4 Ohm and 8 ohm.

This means that on a modern Tube Amp today one typically finds 4 and 8 ohm connections, but rarely 16 Ohm. Sometimes they will have a 6 Ohm transformer tap only, this means that anything from 5 Ohms to 8 Ohms will work well.

In some rare cases a tube amp output transformer will come equipped for 2, 4 and 8 ohm connections but the norm is 4 and 8 ohms  today with 16 Ohms in the past.

Today's modern tube amps are pretty fail-safe. The rear connectors are typical of one Common Lead (-) Black and two Red connections (+) that are marked 4 Ohm and 8 Ohm respectively.

Connect (-) Negative Black lead to the common (typically the Black Connection or marked with a small "C". 

Connect (+) Positive Red or Banded lead to the 4 Ohm connection and ready. 

The same goes for 8 Ohm speakers where the (-) connection is the same and the (+) Positive connection goes on the 8 ohm Tap. Just as well 16 and 32 Ohm taps will have the negative lead on a common point and the proper impedance tap represented by a specific connection that displays the impedance value.

One crucial visual check is to dim the lights (or have a way to darken the room completely) and really have a good look at the output tubes when the amp is powered-up.

The telltale sign of serious trouble is the power tube plates when the tubes are in their operational state. This means that you have turned on the amplifier and you also have some music playing through the AUX, TAPE INPUT, TAPE MONITOR or TUNER inputs. All of these are high level inputs and are as such electrically equivalent.

A Portable CD player with Radio Shack RCA to 1/8" Stereo jack conversion cables are great for this purpose. You can set the output volume level of the portable CD player to check your amp independently from the amp itself (avoids possible shocks). One should set the amplifier's volume control between 9'oclock and 12'oclock position. 

Examine the output tubes when the amp is running and you should see the bright filament that runs through the center of the tube, maybe some light blue haze through the small holes on the plate and the overall look of the tube should be one of bright relaxation.

Now, the signs of trouble are when the large metal structure that is in the center of the tube (called the Plate) begins to show signs of glowing red (like a piece of charcoal on a BBQ.) If you see any signs of the Plates glowing red after let's say 45 seconds or more of the amp being turned-on, immediately turn off the amp.

Glowing plates are an indication of serious trouble. The cause of red-glowing plates may be related to several things, and often multiple conditions at the same time.

Here is a good web link to the internal structure of a Vacuum Tube. Look at the 3rd item, this is what I am referring to as the Plate the large grey or black metallic structure inside the center of the glass tube. 

If this metal structure starts to glow a deep charcoal-red, ..........trouble. Best seen in the dark with the lights out and good access to the power switch. Always a good idea to use a power strip with an On/Off switch for testing purposes. Often vintage amp switches for power on/off can break after repeated use, the plastic gets weak over time.

Here's a link to the internal structure of a Vacuum Tube.

Red Tube Plates may be indicative of but not limited to one of the following

  1. Weak output tubes (end-of-life)
  2. Defective 'Fixed Bias' voltage control wiper or incorrectly adjusted bias voltage
  3. Defective diodes or bridge rectifier causing incorrect bias voltage settings
  4. Shorted 'Cathode Bias' resistor (very rare), resistors typically 'open' not 'short'
  5. Excessive 'plate voltage' due to inadequate power supply loading (open power supply section)
  6. Un-balanced output power tubes (Push-Pull amps) causing current hogging towards one tube
  7. Defective Coupling Capacitor (conducting DC or completely open circuited
  8. Dirty, Loose or Intermittent tube sockets (worn-out)
  9. Cold solder connection(s), broken wires or connections never soldered (common in PC boards)
  10. Incorrect output power tube or driver tube substitutes (very common in amps using EL84 that need 7189)
  11. Boosted mains voltages Vusa>120 VAC (Veu > 240 VAC) causing secondary transformer voltages to boost 15 to 30% 
  12. Bias currents and plate dissipation beyond the capability of the tube (i.e. Ei nipple-top EL34's), "slimmies" can't take the load 
  13. Some other strange but true issue (write to us and tell us about it!)

Here is a link to probably the BEST best single troubleshooting web page.

In the world of electronic troubleshooting pictures, diagrams and real-life experiences are the best medicine. Visual aids help formulate solutions to common and complex problems. Visual inspection is your best line of defense, and learning how to see problems is a great troubleshooting tool. Text alone cannot truly convey some facts, that is, 'bench-time' is the most important weapon in a troubleshooters tool box. It's like flying a plane, you have to begin logging hours on the bench, or else leave this hobby in utter frustration. It's been 8-1/2 years so far and I am still learning new things.

Here is an interesting links to capacitor reforming. If you plan to do lots of Vintage Amp testing, such circuits and methods will save trouble, time, fuses and transformers.


I cannot leave this section without offering to you some ideas on getting the best sound from your tube stereo system. This brings us to the tweaking section which is a controversial area. Yes you can achieve much better performance by adding some accessories to your stereo system.

Power Conditioners

You have probably heard about companies who sell and market AC Power Conditioning components. Often there are claims that these are required to achieve the best possible sonic circumstances. Well I can say that these devices serve a higher purpose than just removing noise from the AC that feeds your equipment, they PROTECT your equipment, and this should be the main reason to spend $300 to $1200 dollars on a multi outlet power conditioning device. Whether they make a real difference in the sound is probably too subjective a Hi-Fi thing for me to delve into at this point. But they offer better protection from surges, spikes and other things that can permanently and fatally damage your precious stereo equipment. Transcendent Audio offers a Balanced Power solution that converts your 120V mains into a 3 wire balanced power. This eliminates "common mode" AC line noise and can have a dramatic effect on the quality of your resulting sound. Monster Cable and other companies offer Power Conditioning solutions. Give them a look. For entry level applications, the ADCOM ACE-515 is an excellent starting point, but it only has 3x3prong outlets and 5x2prong outlets. For those with all 3 connector AC cables as the majority, best go with a unit that offers standard US duplex outlets. The ultimate solution is to convert single phase power to balanced power. There are several products that perform this conversion and they are worthy of a complete web page.

Speaker and Component Cables

Cardas, Cardas and more Cardas. Although I can't afford the Neutral Reference Speaker cables from Cardas at this time, after hearing what these cables can offer, I recommend that you purchase the best speaker cables that you can afford. Currently I am using Van Den Hull JADE cables that are far better than the Linn K20 and the QED 25th anniversary cables that I also own. It also helps to lift all of your cables from the floor. You can build small stands that suspend your cables from direct contact with the floor. If you have hardwood flooring then it's not such a bid deal. But cement and tile floors can use some sort of isolation pieces to help your music be at it's best. Technically I cannot say why, but it just sounds better. All RCA connections should be made with the best cables you can afford. I find Audioquest to be in my price range. Yet other more esoteric cables are available if you want to spend the $. Be careful on vintage components whose RCA inputs may not accept some modern RCA cables as the connectors are often very large and cannot exist side by side without pressing against each other.

Vibration and Damping Control

Without getting too esoteric, Maple is a great wood for you to place under your equipment. The use of a wooden base helps to dissipate vibrations and resonances, rendering a sweeter sound overall. Pine also works as an entry level wooden base. But Maple is by far the best. Look for Maple Cutting boards in stores like Marshall's and Macy's. Advertised among the pages of Hi-Fi magazines are solutions that claim to improve the sound of a stereo system by using pieces of African Ebony, Solid Metallic Spheres and any number of physically diverse materials and combinations thereof. My only advice, experiment first with home-brew solutions before spending any hard cash on these esoteric solutions. Vibrapods, Sorbogel and other damping and vibration absorbing products help alot. Try these out and let me know what improvements you can notice.

CAIG Labs chemicals

ProGold, DeOxit and Cailube are the three basic chemicals (other than alcohol whether for cleaning or drinking) which can fine tune your connections (and ears) to their very best. Older tarnished phenolic screw strips can use a DeOxit. Newer RCA cables and connections call for a dose of ProGold. Finally vintage noisy controls can use a spraying of Cailube. This is a wonderful chemical that both lubricates and quiets noisy potentiometers. Radio Shack now sells DeOxit and ProGold as a pair for 17 bucks. I highly recommend these Caig labs products. Far better than the traditional contact cleaners they are the standard by which all others are measured. The only real way to enhance the conductivity of RCA and Speaker connectors safely is with Caig products. After all, DeOxit is based on the tried and true 'Cramolin' used since the mid 1900's to clean and enhance electrical contacts. But I cannot say that they are the same chemical, this would be conjecture on my behalf. But DeOxit is great stuff and so if ProGold.

Power Cables and Interconnects

If your equipment accepts standard power cables (just as found on most PC monitors and computers) you have a wide array of special products to choose from. Also the RCA and XLR audio cables can also be upgraded with some pretty fancy and excellent sounding products. In this area you can spend anywhere from $35.00 to $4000 dollars. Be careful with Vintage Audio components as often the design of the female RCA input and output connectors are spaced so close that some fancy cables will not work. Audioquest, Cardas, StraighWire and ZuCable are some of the names that come to mind. Most vintage amps come with power cords that are nothing more than 18 gauge Lamp Cord. Upgrading to 16 Gauge stranded, or even 14 Gauge will make a dramatic sonic difference. Just yesterday I walked into Home Depot and picked up 12 ft of 16 Gauge, 2-wire Super-Service with a Heavy Duty 2 prong Levitton plug. I got home, installed the the plug on one end of 6 ft and the other end was soldered into my Harman Kardon A500 and A700 amps. The sonic improvement was astounding. The original AC power cord was 18 gauge, and probably very resistive after +40 years of sitting around. Hear me and believe that the power cord does make a big difference. Now I have to upgrade my ST-35, ASP-422, APH-50's, A300, etc.. etc...

Room Acoustical Treatments

This is the other 1/2 of your speaker system, really. Untreated music rooms will always and I mean always have some sonic phenomenon that affects the sound in a negative manner, in other words things that can be corrected. This subject is both complex and hard to grasp so read, research and read. Simple tweaks such as SONEX panels on the rear walls for a L.E.D.E. (Live end Dead end) are simple and effective. I have used this in a very small den room of mine with good results. Basically the SONEX panels absorb all sound above 1KHZ. This eliminates the bouncing of the sound from the rear walls and makes the wall 'dissappear' so to speak. Also smaller rooms can suffer from Bass Modes while larger rooms can also exhibit echo, delay and room mode problems as well. There is no single tweak that can have more of a dramatic effect on your listening pleasure than treating your music room acoustically. The web offers many sites with good advice and ideas for things like carpeting, helmholtz resonators and other devices easily built with wood and sweat. Also small SW programs exist that can predict room behavior for as low as $99 dollars. But if the room is not rectangular, the software can become much more expensive and harder to learn. In the 90's I used a SW called "Sitting Duck" that was shareware. The purchased version of "Sitting Duck" offered more functionality and the ability to save files. Any way you look at it, a $99 dollar Boom Box will perform better in a treated room, or any audio system will sound better, often much much better. If you are a physics major, the mathematical formulas are easier to grasp. If not, just let the PC and a tape measure do the work. Special recordings and sound level meters are also available so look around. Go to to begin your journey into room acoustics and treatments, you may be surprised...

Audio Racks

I recommend audio furniture for tube amps be that of an open, sturdy and well ventilated design, hence Open Rack systems, never the enclosed furniture types. One can put together a 'poor-man' setup by purchasing long threaded rods, a bunch of compatible washers and bolts, and good maple cutting boards (large enough to accomodate components.) With a good wood drill bit, put a hole in each corner of the maple boards at precise locations. A drill press and clamps will help make this align to perfection. Then assemble the rack with the threaded rods and space as required. This makes for a very elegant and simple system for years to come. If you like 2x4's and plywood, you can also assemble and veneer a rack. Be creative or be spending some real money. Bell'o, Lovan, Billy Bags and Sanus make great looking and functional racks at reasonable prices. Look around, but remember the WAF (Wife Acceptance Factor), HAF (Husband Acceptance Factor) and BFF (Baby Functionality Factor) when you buy your audio furniture :)

Final testing and tweaking

There are setups and there are setups..... I wanted to share one experience so that you are aware of the weakest link philosophy, one which I not only believe in, but have been the victim of more than once. There are those who say that the source is the most important part of any audio system. Start with a bad signal and end-up with mediocre sound. Well I take this one step further. Anywhere in the musical chain where music signals encounter a mediocre connection, poor RCA of XLR contacts, poor pre-amplification, bad amplification, non-performing speaker cables, resistive power cord, noisy AC lines, ground loops, lousy speakers, etc...

I mention all of these, and there may be lots more for a specific reason. More than once, I have encountered bad sound, or should I say a noticeable degradation in the quality of reproduced sound. More often it has been that one set of speaker cables sounds much much better than some other pair I own. A simple swap like a wipe with Windex on a dirty window pane. Other times it has been an aging set of power tubes in an amplifier that slowly make the music more fatiguing and less interesting.

So.... the story here is simple. If you want to build the best sounding setup, start simple. Then as the evening goes by, progressively add additional components.

You can start by running a CD player direct into the amplifier (if the player or amp have some means of controlling the signal levels) and then hookup the speakers with clean, tight connections.

Play some music and start to swap cables, move the speakers around the room and experiment with your seating position and also the height of the speakers. Once tweaked-in, then you can start to add the Preamp and test for differences. It's all about tweaking your setup for the best sound.

Try using rugs and window treatments. Things in the room can vibrate so also pay attention to distortions. It's all worth the trouble as your final reward will be a much better sounding music setup.

Remember that you may have to eventually re-check all of the connections on your stereo system to make sure they are secure, tight and properly connected.



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