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 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'
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....
You will hoover over ideas and wants, while enjoying simpler Home Tube Amps...
Prima Luna, McIntosh, Luxman, DecWare, Rogue, & Kit Amps.
If you spend, spend wisely.
If you want to learn how to fix these amps, you have to invest time and money
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?
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. CALLED GAIN SCALING.
THEN YOU CAN HAVE THE JOY OF USING "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
SO IF YOU CANT AFFORD A 300B TUBE AMP OR PREAMP, 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, BUT I HAVE
BUILT THREE KITS AND STILL OWN AND ENJOY THE PHONO STAGE)
OLD TUBE AMPS ILLUSTRATED
TOP AMPLIFIER MODELS OF THE DAYS OF YORE
THE "GRANDPARENTS" OF TUBE HOME AUDIO ARE COOL AGAIN
A.A.R.A. = AMERICAN ASSOCIATION OF RETIRED AMPS
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.
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..
THE 8417 WAS A FART IN A HURRICANE OF SOLID STATE MARKETING
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
BIG BOLD BRASH...
Bob even designed "Receive Diversity" FM Car Stereos.... WTF?
Have you ever heard of the Carver MAGNETIC FIELD AMPLIFIER?
FM Stereo Receive Diversity?
Juet 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
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
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;
#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
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)
DECWARE IS CLASSIC POINT TO POINT HANDMADE OLD SCHOOL PURITY (BARGAINS)
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
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
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....
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.
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.
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.
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
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.
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
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
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.....
#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
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.
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.
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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