A view from the inside

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 26 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 towards the future.......

Classic Tube Amp Internet Safari

Your guide to the Classic Tube Amp online jungle

'Watch out for Dodo-Bird Amplifiers'

Good for Movie props on 40's, 50's & 60's films

or for living off a stash of "end-of-the-world" Tubes are the Dodo Bird Amps.

Some old Dodo Bird Amps under deliver in the Musical Departments

so that the not all Tube Amps were created equal... is this true, sometimes it is.

Or... if the tubes are more expensive as putting 4 new tires on both your Cars.

Be aware that some Exotic Tube Amps may need "expensive" Tubes.

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.

You will hoover over ideas and wants, while enjoying simpler Home Tube Amps...

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

If you want to avoid a Dodo Bird experience,  spend wisely.

You may just want to challenge yourself

 to build a Tube Preamplifier Kit?

HOW ABOUT A MASTERPIECE?

THE 300B - TUBE AUDIO SOUL OF MUSIC

LIFE, COLOR, TEXTURE AND TONE

HOW ABOUT FIDELITY?

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

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

IF YOU WANT A GENEROUS SLICE OF TUBE AUDIO PIE

WITH A DOLLOP OF FRESH IRISH CREAM.... AND YOU LOVE HEADPHONES......

THIS PREAMPLIFIERS & HEADPHONE AMPLIFIER SERVES UP A DELICIOUS SONIC BUFFET

JUST CLICK ON THE 300B KIT ABOVE, TO VISIT TRANSCENDENT SOUND

LOOK AT THE REFINED D.I.Y. KITS, AT VERY REASONABLE COST LEVELS

TRANSCENDENT IS A PROBLEM SOLVER AND THERE ARE SOLUTIONS

TO MANY TYPICAL ISSUES WITH TUBE HOME STEREO

THE PREAMPLIFIER PRODUCTS ALONE OFFER THREE DISTINCT

BUNDLES FOR MAXIMUM PERFORMANCE TO MAXIMUM ADAPTABILITY.

THE SLIDER PREAMP ALLOWS ONE TO COMPENSATE FOR ANY

UNWANTED OVER-DRIVEN SIGNALS, MAKE EVERY

INPUT OUTPUT CONNECTION MUSICAL.

THEN YOU CAN THE POWER OF TRUE TREBLE AND BASS CONTROLS

NOT THE RESISTIVE PAST, BUT AN ACTIVE WAY TO CONTROL TREBLE

AND BASS TO ASTONISHING LEVELS AND DRIVE A SUBWOOFER

AT THE SAME TIME.

THE 300B DHT TRIODE TUBE IS THE "STANDARD" OF HOW TUBES PORTRAY MUSIC

RICH, CREAMY, HARMONIC AND NATURAL

IF YOU CANT AFFORD IT, JUST BUILD IT!

YOUR HEADPHONES ARE WAITING.....

IF YOU PREFER TO HAVE ONE ALREADY BUILT

YOU CAN INQUIRE ON THE TRANSCENDENT WEBSITE

FOR RECOMMENDED TUBE AMP BUILDERS

(NOT AFFILIATED - TRANSCENDENT SOUND - NO CONNECTION WHATSOEVER)

TUBE AMPS ILLUSTRATED

TOP AMPLIFIER MODELS OF 2022

THE "GRANDPARENTS" OF TUBE HOME AUDIO ARE COOL AGAIN

A.A.R.A. = AMERICAN ASSOCIATION OF RETIRED AMPS

 I now displat 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

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

Dynaco MK6's Monoblocks - 120 Watts - Monoblocks

('defunct 8417 Power Tubes')

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

THESE ARE IN THE DODO BIRD AMP CATEGORY

THE 8417 TUBES CAME OUT WHEN SOLID STATE WAS EMERGING

THEY NEVER HAD A CHANCE AGAINST THE SOLID STATE MARKETING WAVE...

Carver Silver 7's - 375 Watts - Monoblocks

Bob Carver the Tube Wizard

https://www.bobcarvercorp.com/

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

This is Bob Carver, He loves to do things HIS WAY

BIG BOLD BRASH...

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

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

I actually enjoyed once the Jolida 3000A at Rocky Mountain Audio Festival in 2004

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

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

I took some video, so I will try to digitize and post it here for your enjoyment of the Jolida's

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 switch between Modes.

McIntosh MC3500 - 350 Watt Monoblocks

I once saw a pair of these at Sprat Hall in St. Croix.

The Holy Grail of McIntosh Tube Amps

These started a small revolution in "High Power" Tube Audio

CAVEAT: YOU NEED QTY-2 for STEREO OR ONE HUGE SPEAKER!

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.

So.......

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.

Superposition

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

Time

DON'T LOSE HOPE....

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

PRIMA LUNA IS LEADING EDGE NEXT GENERATION TUBE TECHNOLOGY (COMPETITIVE)

https://www.primaluna-usa.com/

DECWARE IS CLASSIC POINT TO POINT HANDMADE OLD SCHOOL PURITY (BARGAINS)

https://www.decware.com/newsite/homepage.html

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

http://quicksilveraudio.com/amplifiers/

SO YOU STILL INSIST ON AND DESIRE A CLASSIC AMP? READ ON...

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"

BID/PAY ACCORDINGLY, ASSUME IT IS BUSTED

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...

That my friends IS A TRUE MOLESTED AMPLIFIER!

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....

HALLICRAFTERS S-38C

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

https://www.cemfg.com/

AUDIO FORUM CAVEAT

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.

https://dynacotubeaudio.forumotion.com/t4913-mark-3-fuse-blows-after-hours-of-use?utm_campaign=popular&utm_medium=topic&utm_source=newsletter

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

HERE IS LOGICAL ROUND OF QUESTIONS, TO HELP THE PERSON WITH THE UNHAPPY AMPLIFIERS

"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"

THE PERILS OF DOGMA & BELIEF SYSTEMS

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!

LEAVING TUBE EQUIPMENT ON, AND BE ABSENT, A NO-NO.

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)

SOME POWER TRANSFORMER SECONDARY & CATHODE RESISTORS- 3 VICTIMS

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...

OUTPUT TRANSFORMER PRIMARY -  2 VICTIMS 

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

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!

THAT ALL ORIGINAL CLOTH WIRE POWER TRANSFORMER

IS EXPECTING 115 VAC, NOT 120/125VAC

YES, ONLY THREE TO FIVE VOLTS AC MAKES A DIFFERENCE

Visit my Tube Amp Spa for treating this Classic Amp affliction

OLD DYNACO POWER TRANSFORMERS WERE BUILT WITH LITTLE HEADROOM

SO EVEN AT THEIR CORRECT PRIMARY VOLTAGE

THEY RUN

CALIENTE, AND OFTEN HAVE MECHANICAL VIBRATIONS

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.

http://www.tubes4hifi.com/ST70.htm

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...

NOTE THE 6AN8 IS NOT A 7199 SUBSTITUTE

THE 7199 HAS NO SUBSTITUTES

THE LAST KNOWN VERSIONS WERE MADE IN

RUSSIA AND OUT OF 10 TUBES

6  MAY WORK, THE REST BUZZZZZZ

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....

I MADE ALL OF THESE MISTAKES ALREADY FOR YOU!

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

HARMAN KARDON A700 TUBE AMP MEDICARE CARD

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)

Craigslist

Grandparents/Parents/Aunts/Uncles/Cousins

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!

SOMETHING ABOUT THAT MARSHALL STACK BUzzzzzz

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"

THE HASSLES OF CLASSIC TUBE AMPS

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

 DC & AC FILAMENT VOLTAGE BOOST

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

THE DREADED RED PLATE SYNDROME

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...

DO NOT USE CONTACT CLEANER ON POTENTIOMETERS DEOXIT, PROGOLD, ETC. NEVER EVER, EVER.....

IF YOU DO HAVE CAILUBE OR PROPER POTENTIOMETER LUBRICANT SPRAY CLEANER YOU CAN "RISK" SPRAYING OLD POTS

BETTER TO ORDER NEW BOAS POTS, AND CHANGE THEM OUT, THEY ARE OLD AND SAVE YOUR TUBES

ALSO WHEN YOU SPRAY POTS ALWAYS SURROUND THEM WITH PAPER TOWEL SO THE SPRAY DOES NOT PROPAGATE

OLD CARBON POTS SUFFER FROM CONTACT CLEANER SPRAY AND OFTEN, CRACK DUE TO THE MOISTURE CONTENT

IF A POTENTIOMETER IS SCRATCHY AND POTENTIOMETER SPRAY DOES NOT HELP, REPLACE IT.

INSPECT ALL OLD PC BOARDS FOR CRACKS AND/OR CRACKED TRACES

EXAMINE ALL POWER TUBE COUPLING CAPACITORS FOR COLD SOLDER CONNECTIONS

REPLACE ALL OLD COUPLING CAPS WITH NORMAL ORANGE DROPS OR YELLOW POLY CAPS, CHEAP INSURANCE

OBSERVE THE INNER AND OUTER FOILS, COUPLING CAPS OUTER FOIL (BANDED END) TO THE INPUT

RETENSION TUBE SOCKETS WITH A SMALL NARROW AWL CAREFULLY & GENTLY ONLY IF NECESSARY

TEST THE POWER TUBES, AND IF IN DOUBT, RELOCATE THEM TO DIFFERENT SOCKETS

MEASURE THE BIAS VOLTAGE IF THE AMP IS FIXED BIAS WITH THE RECTIFIER TUBE REMOVED

IF THE AMPLIFIER IS HV DIODE RECTIFIED THEN MAKE SURE THAT YOUR POWER SUPPLY ELECTROLYTICS ARE NEW

IF THEY ARE ORIGINAL THE VOLTAGE ON THE FIRST CAPACITOR WILL EXCEED THE PUBLISHED MAXIMUM

IF YOU DON'T KNOW HOW TO MEASURE THE BIAS VOLTAGE, GO THROUGH MY MEASUREMENTS PAGE

WITH THE VOM BLACK LEAD SAFELY CLIPPED TO DC GROUND, THE VOLTAGE SHOULD BE NEGATIVE (-) AND CHANGE WHEN THE POT IS TURNED

IF YOU CANNOT GET THE BIAS VOLTAGE TO SWING WHEN TURNING ONE OF MULTIPLE THE BIAS POTS, YOU HAVE A BIAS SUPPLY PROBLEM AROUND THAT POTENTIOMETER

IF THERE IS NO BIAS VOLTAGE THEN SUSPECT THE BIAS SUPPLY AS ALL TUBES WILL TURN RED IMMEDIATELY ON POWER ON

ALWAYS, ALWAYS, ALWAYS REPLACE THE SILICONE BIAS RECTIFIER  DIODE AND FILTERING CAP, ALWAYS, ALWAYS

IF THE SAME TUBE GLOWS RED IN A DIFFERENT SOCKET, YOU HAVE A BAD TUBE

DO NOT, DO NOT, NEVER USE CONTACT CLEANER ON TUBE SOCKETS

IF YOUR AMP IS CATHODE BIAS REPLACE THE CATHODE RESISTOR(S) AND BYPASS ELECTROLYTIC CAPACITORS

FINALLY DON'T WASTE YOUR MONEY ON REPLACING SPEAKER SCREW TERMINALS

IF THE PHENOLIC TERMINAL MATERIAL IS CRACKED, ORDER THE SAME REPLACEMENT

THERE IS NOTHING WRONG WITH USING BARE SPEAKER WIRES

THE SOUND IS BETTER WITH BARE WIRES ON A CLEANED SCREW TERMINAL, BELIEVE ME

BUTCHERING YOUR AMP WITH RED/BLACK SPEAKER TERMINALS IS DONE AFTER IT IS ALL WORKING

BY BUTCHERING, I MEAN DRILLING OUT TYHE OLD SCREW TERMINALS FOR MODERN BANANA RECEPTABLES

YOU CAN USE A 000 FINE STEEL WOOL OR A SOFT DREMEL TOOL TO WIPE OFF OXIDATION ON TERMINALS

FORGET EXPENSIVE FANCY SPEAKER CABLES ON VINTAGE AMPS SAVE YOUR MONEY USE MONSTER XP AND SPADES THAT FIT

ABOUT TUBE ROLLING AND EXTENDING TUBE LIFE

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

COMMON OLD CLASSIC TUBE AMPLIFIER POWER TUBE FAULTS

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 ARE NOT HANDY WITH ELECTRONICS FIND A TUBE TECHNICIAN

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.

CLASSIC AMPLIFIER GAIN, How & Why?

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

 GAIN SCALING & INPUT OVERLOAD

ON CLASSIC AMPLIFIER INPUT OVERLOAD...

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

ON GAIN SCALING

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

PAS2/3/3x

DYNACO PREAMPLIFIER

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"

ON THE SUBJECT OF LEFT AND RIGHT CHANNEL IMBALANCE

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..

KENNY ROGERS ROASTED VOICE COILS

Did you ever wonder, after letting loose and flooring your

UN-MOLESTED CLASSIC amp/preamp...

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.....

https://en.wikipedia.org/wiki/Capacitor_plague#/media/File:Blown_up_electrolytic_capacitor.jpg

 #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...

https://tubeworldexpress.com/pages/contact-us

Jim McShane...

http://www.mcshanedesign.net/

Brent Jesse...

https://www.audiotubes.com/

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.

NOT IN YOUR AMP, IN YOUR TUBE TESTER

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)

ALSO IMPORTANT TO UNDERSTAND

When you use fresh brand new tubes

REALIZE, THIS IS HOW YOUR AMP REALLY SOUNDS

AND LET THE TUBES PLAY FOR A FEW MONTH'S

UNTIL THEY SETTLE DOWN

DON'T ROLL NEW TUBES

THIS IS FOLLY

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"

WE REPEAT THE LESSON AGAIN, FOR REINFORCEMENT

Class, now repeat after Me...

#1 - CAPACITORS & OLD RESISTORS

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

#2 - POWER SUPPLY (PSU)

Replace ALL voltage dropping Resistors & Rectifier Diodes

Don't be a cheapskate

#3 - CLASSIC OUTPUT TRANSFORMER CAVEAT (a.k.a. OPT)

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.....

CLOSING STATEMENTS

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 25 Watts

"The Tinder Tube Amp Partner Search"

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

The Tinder Hopefuls > 8 Ohm Millennials

Those kinky Tinder Boomers > 4 Ohm Retiree "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.

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