MUSICAL INSTRUMENT TUBE AMP BUILDING, MAINTAINING AND MODIFYING FAQ
Much of this material applies to building or re-building hi-fi equipment,
as well but it was originally intended for musical instrument crazies.
Assembled by R.G. Keen, keen@eden.com
Most recent revision level is Version 1.07, appx. 2/28/96
Changes from the previous version are marked with a ">"
==============================================================================
Special thanks to the contributors who made this possible:
Hundreds of folks who taught ME stuff when I didn't know a triode from a
Tri-Axis; I can't remember all of your names, and it all comes out as
general knowlege now, but I appreciate it. A few names in that category
stand out:
Tom Balon, balon@cup.hp.com
David Mourning, dam@dcs.gla.ac.uk
Mark Hammer, no longer on the net that I can find
And people who have contributed things that I have included as part of
the actual text:
Dennis O'Neill, denio@seismo.css.gov
Nathan Stewart, npstewar@eos.ncsu.edu
George Kaschner, gckaschner@ucdavis.edu
David Kohn, kohn@SCTC.COM
Michael Edelman, mje@pookie.pass.wayne.edu
Len Moskowitz, moskowit@panix.com
Tremolux@aol.com
Brian Carling, brian.carling@acenet.com
Eric Barbour ebarbour@netcom8.netcom.com
=========================================================================
INDEX
> 0. *** SAFETY WARNING *** READ THIS FIRST!!!!!
1. Why is AMP building in a musical instrument building group?
2. Where can I learn about building tube amps?
3. Where can I find parts to build/repair amplifiers?
4. How can I modify my amp to be more powerful?
5. How can I extend my tube life?
6. How do I get...
- blues distortion?
- Marshall/metal/Boogie/etc. distortion?
- good distortion at low(er) volumes?
7. Where can I find plans for a Belchfire/Maximo/etc. speaker cabinet?
8. Output transformer questions:
> A. How can I tell if my output transformer is live or dead?
> B. Where can I get a good replacement output transformer?
C. I want to make my own power and output transformers. How do I do
this?/ Where can I find information about this?
> D. Should I replace my stock transformer with a new/old/vintage/purple
> one for better clean/grunge/grit/etc. sound?
9. What is the easiest way to get tube sound at a good price?
10. How can I modify my tube amp to ... ? (also see recommended mods, below)
- get lower hum?
- have higher gain/more distortion?
- have a smoother, less buzzy distortion?
11. When should I bias my amp and how do I do this?
A. What is "bias"?
B. When should I bias my amp?
C. How do I bias my amp?
> D. Matched output tubes - do you need them?
12. Amplifier Modifications
A. Recommended amp modifications
> B. OK but involved modifications
C. NOT Recommended amp modifications
13. Tube Characteristics and substitutions
>14. Maintenance (Still under construction, pretty thin right now)
Appendix A. Tube Stuff Suppliers
Appendix B. Tube Makers Producing Today (Eric Barbour news posting)
=========================================================================
> 0. *** SAFETY WARNING *** READ THIS FIRST!!!!!
> Working inside a tube amplifier can be dangerous if you don't know
> the basic safety practices for this kind of work. If you aren't
> prepared to take the time to learn and apply the right precautions
> to keep yourself safe, don't work you your own amp. You can
> seriously injure yourself or get yourself killed. This section is
> not intended to be a complete guide to safety in tube equipment,
> just to hit the high points as refresher for those of you who have
> some experience. The best way to learn the requirements and
> practices for safety in tube equipment is to find someone who will
> teach you one on one.
>
> BASIC REQUIREMENTS
> - UNPLUG IT FIRST
> Pretty self explanatory. Do not, ever, ever, leave the equipment
> plugged in and start work on it. Leaving it plugged in guarantees
> that you will have hazardous voltages inside the chassis where
> you are about to work. This is like setting a trap for yourself.
>
> - LET IT DRAIN
> If the amp has been turned on recently, the caps will still have
> some high voltage left in them after the switch is turned off.
> Let it sit for five minutes after you turn it off.
>
>
> - SUCK IT DRY
> When you open up an amp, you need to find a way to drain off any
> residual high voltage. A handy way to do this is to connect a
> shorting jumper between the plate of a preamp tube and ground.
> This jumper will drain any high voltage to ground through the 50k
> to 100K plate resistor on the tube. To do this successfully, you
> will need to know which pins are the plate pins. Look it up for
> the amp you're going to be working on. You'll need to know this
> for the work anyway. Leave the jumper in place while you do your
> work ( high voltage electrolytics caps can "regrow" voltage like
> a battery sometimes. Really. ) Remember to remove it when you
> finish your work.
>
> - TEST IT
> Take your multimeter and ground the (-) lead. Probe the high
> voltage caps and be sure the voltage across them is down,
> preferably to less than 10V.
>
>
> - BUTTON IT BACK UP FIRST
> Take the shorting jumper out. Put the chassis back in the
> cabinet, making sure all of your tools, stray bits of solder,
> wire, etc. are out of it. You don't have to actually put all the
> screws and so forth back in if you believe more work might be
> needed, but make sure that the chassis is sitting stably in the
> cabinet and won't fall out. At the end of a listening test,
> either continue buttoning up if you're done, or go back to
> UNPLUG IT FIRST.
1. How is an AMP a musical instrument?
For electric guitars, basses, and possibly other instruments, the amp
is as much a part of the final sound as the nominal instrument is,
perhaps more. The instrument is relegated to a role of providing a
base tone which is profoundly modified by the following effect and
amplification stages. The "instrument" is properly the instrument and
amp together.
2. Where can I learn about building tube amps?
> Get one or more of the following references (note that these books
> are mostly old, and highly sought after, and so may be expensive and
> hard to find):
> - "The Ultimate Tone" by Kevin O'Connor. This the best book on
> guitar amps I've found. It assumes you know some electronics
> to start with, so is not a beginner's book. Published by
> Power Press, which now has a web page at
http://www.wwdc.com/~power/ .
- "The Tube Amp Book" by Aspen Pittman, now in its fourth edition.
This contains the majority of guitar amp schematics ever made.
- "Electric Guitar Amplifier Repair Handbook" (?) By Jack Darr. Good
intro to actually making repairs as well as many schematics.
- "ARRL Handbook", preferably a late 60's or early 70's edition. Read
the sections on construction practice, safety, and tube info.
- Guitar Player Magazine's article on tube types and operation from a
year or so ago
- Glass Audio magazine, Old Colony Sound in Peterboro NH
- Mesa/Boogie will send schematics of their amps, call 1-707-778-6565;
note however, that these schematics are known to be innaccurate.
- "Vacuum Tube Amplifiers" by G.E. Valley, Jr. Part of the MIT
radiation lab series, originally published by Boston Technical 1964.
Reprints are currently available from Antique Radio Classified (P.O.
Box @, Carlisle, MA 01741, 508-371-0512)
- Amplifiers, H. Lewis York.
(Evidently part of the Encyclopedia of High Fidelity). Good basic
technical ref. Simple math, good explanations. Includes a couple
of designs (several use hard to find tubes) and tips on phyiscal
construction as well.
- Radiotron Designer's Handbook, Langford-Smith. Heavy theory, heavy
technical. Not coffee table reading, but it you want to know, it's
probably in there. (Rumoured to be divinely inspired - if not the
Bible on vacuum tubes, it's at least Leviticus.)
- The RDH is available on a CD from Old Colony Sound!!!!!!!!!!!!1
- RCA Receiving Tube Manual. Reprints available from several sources,
including Antique Electronic Supply & others (Old Colony?) Mostly
tube spec sheets & some charaterstic charts. The intro is a pretty
good technical primer.
- Electron Tubes, R.G. Kloeffler. little application, but a good easy
to digest explanation of charateristics of diodes, triodes, beam
power & true pentodes, with the math to go along. Worth reading if
you're trying to do modeling.
- The Audio Designer's Tube Register. Tom Mitchel. 1993, Media
Concepts. Volume 1 - Common Low Power Triodes. 144 pages of
freshly compiled tube data, some of which was not previously
published. Kinda pricey ($18 from Antique Electronic Supply) unless
you need the data. Included are plate characteristcs, tranfser
characteristics, constant current curves, mu as a function of grid
potential and plate potential, transconductance as a function of
plate current and grid potential, and dynamic and static plate
resistance as a function of plate potential and plate current.
(Tom mentions a 2nd and 3rd volume in the distant future - covering
low power pentodes & oddball tubes, and Power & Beam Power pentodes
respectively.)
- Learn about the manual and safety aspects of working on tube
amplifier circuits. Read the ARRL handbook, or better yet, get to
know a ham radio operator who will give you some guidance and
teaching. Do not skimp on the safety aspects. Tube circuits
contain deadly voltages. You can - * DIE * - if you mess up or are
careless. It is your personal responsibility to learn how to do
this safely.
- Get to know a guitar repair technician, perhaps do some free
apprentice grunt work for them in return for some teaching.
3. Where can I find parts to build/repair amplifiers?
New tube parts and supplies are steadily getting harder to find, but
paradoxically, used parts are often nomimal cost or free. The hard
parts to find are the transformers.
If you're building, I recommend building around what transformers are
available to you. And AFTER you have them in your grubby little
hands. It often happens that the transformers you THOUGHT you would
buy after you got the chassis, sockets, etc. was just sold to another
fellow, and there aren't any of those left... (Stewart)
The easiest but most expensive source for parts is at your retail
musical instrument store. Other sources:
- Musical instrument repair shops will sometimes order parts or sell
you parts out of their stock.
- Amp makers' repair parts departments. Many manufacturers will sell
their parts to "repair shops" to fix their amps. Some of them are
better than others about this, so be polite and businesslike.
- Antique Electronics Supply, Tempe AZ. They stock tubes, some
transformers, some capacitors, tube sockets, etc.
Antique Electronic Supply recently added several steel and a few
aluminum chassis boxes to their line. I was told this is to be a
continuing trend, and not just a one time buyout of a couple of
boxes.
- Mouser and SESCOM (don't have the address/phone) sell various
rack enclosures. Mouser has a couple which would house a healthy
size tube amp project.
- old, broken, or unloved equipment. This may be free, or
units-of-dollars. You get transformers, sockets, tubes, and chassis
in the deal. May require cruising garage sales or diving in
dumpsters. Trash every part except the tubes, transformers, sockets
and chassis. I got a 15 Watt mono amp/preamp intended for mono hi-fi
music for $20 at a local garage sale. Needs only some tweaking to be
a Studio .22 or an AC-15.
Be sure to look at Appendix A for more sources.
In some issue of The Absolute Sound (a "high-end" audio mag), Steve
Melkisethian wrote an article called "Where the Tubes Are: Tube Tips
and Topics" [reference lost, sorry, I just have a copy of the article;
it was sometime in 1987-1992). The article obviously is aimed at the
high-end hifi market, not at guitarristas, but he lists some of the
following sources, with various cautions (see the article for more
info).
SM called the following "premium suppliers":
o Fender Musical Instruments - call 800-854-6230 for a list of
dealers
o Richardson Electronics - 800-348-5580 for dealer list
o RAM Tubes, 805-962-4445
o VTL, 714-627-5944
Here are "more tube supply sources":
o Triode Electronics, 312-871-7459
o Elmiria Electronics 800-847-1695
o Antique Electronic Supply, oriented to radio collectors,
602-820-5411
o Antique Audio, oriented to radio collectors, 512-467-0304
o New Sensor, mostly imported tubes (here's the source of Sovtek),
call Mike Mathews, 212-980-6748. Min. order is $50.00.
o ARS Electronics, 800-422-4250
o Department of Defense surplus auctions. DRMO-Tobyhanna Army Depot,
Building 16, Tobyhanna, PA 18466 is the gummint storage facility
for communications gear and is said to have good stuff. Also,
get "How to buy...Surplus Personal Property from the Department of
Defense", free from DOD Surplus Sales, PO Box 1370, Battle Creek,
Michigan 49016.
o Surplus electronics dealers - see the Telco yellow pages
o call everybody in the yellow pages under Electronics, TV-Repair,
Communications, and any other promising category.
o Hamfests
o SM's store, Angela Instruments, 8600 Foundry St. Box 2043, Savage,
Md. 20763, 301-725-0451.
o Tube Amp Service in San Francisco,run by Tom Balon; call
415-334-5200 PST. (O'Neill)
George Kaschner notes that parts other than tubes and transformers
can be obtained easily from Mouser Electronics (800-346-6873). I have
used Mouser and they give good service and prices; $20 min order.
another good source is Digi-key for resistors, capacitors, and other
general electronic parts. They are not tube oriented, but are also
a good general parts source.
4. How can I modify my Blender Tweety Bird amp to be as loud as a
Marshall Major/AC30/Tweed Bassman/SVT/etc.? (Alternatively, how can I
make my amp twice as loud/more power/ etc.?)
You can't do this in a low power amp, at least not electronically. To
put out the power the big amps put out, you need the entire power
train to be as beefy as the big amps. This means bigger power
transformer, rectifiers, filter capacitors, output transformer, more
power tubes, bigger chassis, more ventilation to carry off the heat,
lots of things. You can't just add a couple of tubes.
> An amplifier is properly thought of as primarily a big power supply
> that has some extra junk tacked onto it to carefully let a little of
> the power out to the speakers under special, controlled circumstances.
You might be able to just pull a couple of tubes OUT of a high power
> amp to make it quieter, under some conditions. O'Connor discusses
> this in "The Ultimate Tone".
5. How can I extend my tube life?
- modify the power on switching to heat the filaments first, let them
warm up for 30 seconds, then switch on the high voltage plate supply.
- add more ventilation to the amp chassis, perhaps with a small fan.
- modify the tube operating conditions so the maximum cathode current
is not exceeded under even maximum warp drive conditions. Exceeding
max cathode current causes cumulative emission losses and early tube
death. This requires a somewhat deep understanding of the design of
tube amps to do, unfortunately.
6. How do I get...
- blues distortion? Made by overdriving preamp and power tubes a
little, enough to just start compressing the peaks of the waveforms,
and not very much high frequency content, by electronically cutting
highs or running the signal into a speaker cab that acoustically
cuts highs.
> Guitar Player magazine ran a construction article on this very
> topic, modifying a Fender Bassman to be the "Ultimate Blues
> Machine". The article ran in 1995, authored by John McIntyre.
>
> A recently voiced although intuitively applied idea in
> distortion is that tube distortion sounds best when each
> successive distortion stage is overdriven by less than about
> 12db. This has the effect of keeping the tubes inside the area
> where the signal is more compression-distorted than clipped. That
> is what those resistive divider chains between distortion stages
> are for inside those distortion preamp schematics. Mesa's
> distortion preamps are another good example.
>
> Overdriving a tube stage too much gives you harsher clipping, not
> the singing, sweet distortion we want. To really get sweet,
> crunchy distortion, keep each stage that goes into distortion no
> more than 6-9db into distortion.
- Marshall/metal/Boogie/etc. distortion? Made by massively overdriving
preamp tubes until the original waveform is massively compressed and
clipped. Usually followed with a moderate amount of high frequency
cut to remove some of the "insect attracting" overtones generated
in the clipping process. There is commonly some output tube
overdrive in this process, too.
- good distortion at low(er) volumes? overdrive preamp tubes until you
get the clipping you want, then feed a limited amount of this to a
power amp stage to get the loudness you want. This is how master
volume controls work.
7.Where can I find plans for a Belchfire/Maximo/etc. speaker cabinet?
- ElectroVoice sells (?) makes available (?) plans for cabinets for
their speakers
- copy an existing cab
- some cabinet fitting suppliers have example plans
-- (addresses in a future posting) ---
8. Output transformer questions:
> A. How can I tell if my output transformer is live or dead?
There are some simple tests you can run to quickly determine if a
transformer is grossly bad. This is much simpler than determining
if it will work well and sound "good" for you. The tests of
relative "goodness" are also possible, but require a lot of
equipment and experience to do correctly. For the quick and dirty
tests described here, you'll need a means of measuring AC voltage
and current simultaneously, such as a pair of VOMs or DMMs, and a
110/120 to 6.3VCT filament transformer, and either a variac
(variable transformer) or a light bulb socket in series with the
primary of the filament transformer to limit the power you put into
the transformer under test.
CAUTION
CAUTION
CAUTION
Both the filament transformer and the transformer under test will
have at least AC line voltage on them, an may well have much higher
voltage, several hundred volts on one or more windings. You are
therefore in danger of being KILLED if you are not both knowlegable
and careful about how you do these tests.
DO NOT TRY THIS IF YOU DO NOT HAVE THE KNOW-HOW AND EXPERIENCE TO
WORK SAFELY WITH THESE VOLTAGES. IF YOU HAVE ANY QUESTION IN YOUR
MIND WHETHER YOU CAN DO THIS WORK SAFELY, YOU CAN'T.
Seek experienced help if you have any question in your own mind.
The tests run like this. Identify which wires are which by color
code, circuit connection, or by using an ohmmeter to find which
connects to which. Label the wires. From the same ohmmeter test,
write down the resistances you measured on the windings.
Generally, windings with resistances over a few ohms are high
voltage windings, either a power transformer primary or high
voltage output, or an output transformer primary. Note that it is
common for primary windings on power transformers to have from two
to six wires, with the wires over two being taps to adjust for
various line voltages from 110-117-120-125-208-220-240. Secondary
windings on power transformers and primaries on output transformers
will have either two or three leads, and secondaries on output
transformers will have to to four leads.
Also note if any winding is shorted to the transformer core.
Sometimes an internal shield will be deliberately connected to the
core, but if a multi-lead winding is connected to the core, this is
usually an internal short, and a dead transformer.
Once you have identified the windings, hook up one and only one
winding to either 1/2 of the 6.3VCT or to the variac. Try to
select a low voltage winding, one that has low resistance from the
ohmmeter test. Make sure that no other leads are connected (or
shorted together, or touching your screwdriver on your bench or...
well, you get the idea). A turn of plastic tape on each wire end
you'r not using at the moment is a good idea. Set your voltmeter
on this winding, and the current meter to measure the current
through it, and bring the circuit up. The voltmeter should measure
3 volts AC, the light bulb (if used) should NOT be lit brightly,
and nothing should be humming or smoking ;-). There should be
little current going through the winding. If the voltage is lower
than 3 volts, or you are pulling amps of current, then there is a
load on the transformer, internally since you have disconnected all
the leads, meaning that there is an internal short. You should try
to select a winding for this test that is normally a low voltage
winding, either a filament winding in a power transformer, or a
secondary in an output transformer.
If all is well, measure the voltage that now appears on the other
windings. The voltages will be equal to the ratios of the voltages
that will appear on these windings in normal operations.
> B. Where can I get a good replacement output transformer for my
> vintage DoppelBanger amp?
> Dixie Sound Works, Gunthersville, Alabama has a great reputation
> for (re)winding quality vintage re-makes.
> The company that made the amp may have service parts. The quality
> is variable from company to company and time to time, though.
C. I want to make my own power and output transformers. How do I do
this?/ Where can I find information about this?
- Designing and hand winding transformers is not terribly difficult,
but it does require information and skills that are relatively
hard to find. You are unlikely to save a whole lot of money unless
used or broken parts are cheaply available to you. You may want to
do this if you feel that you were selected by some deity to take
this on as a life work.
- First, take a transformer apart. A burned out tube-type power
transformer will do. Do this carefully and slowly, imagining how
you would have put it together in the first place to get it the
way it was. This is an excellent introduction to the manual skills
and materials needed to sucessfully produce one on your own.
- Learn about how transformers are designed from one or more of the
following, in this order:
* "Transformers for Electronic Circuits", Grossner (check your
library)
* "Radiotron Designer's Handbook, fourth edition
* "Audio Transformer Design Manual", Wolpert, $36, privately
published, available from:
Robert G.Wolpert
5200 Irvine Blvd. #107
Irvine CA 92720
* "The Williamson Amplifier" D.T.N Williamson, reprint available
from Old Colony Sound Labs
* Handbook of Transformer Design and Applications by William
Flanagan (second ed.)
* "rewinding transformers with CAD" by Hugh Wells W6WTU Ham Radio
Dec '86 p.83
* "Fast Optimization of Transformer Design" EDN Nov '62 by Davis,
J. H.
These sources will help. They are NOT a complete cookbook. Note
that it is very possible to make a transformer that will operate
relatively well, but may break down unexpectedly and KILL you if it
is not constructed with safety in mind.
> D. Should I replace my stock transformer with a new/old/vintage/purple
> one for better clean/grunge/grit/etc. sound?
> - Unless you REALLY know what you're doing and have heard the
> transformer you'll be swapping in and like it, no.
>
> There are a huge number of variables in the "sound" of a
> transformer, and you should exhaust other means first. You might
> not get that magic sound after all that work unless your ears
> - and amp tech - are really good.
9. What is the easiest way to get tube sound at a good price?
- Obtain an old piece of tube gear, perhaps intended for another
purpose, like mono hifi, at no or low cost. Modify this to duplicate
to a certain extent the circuit of an existing amplifier. Tinker to
your heart's content.
> There is a document on exactly this at
> http://www.wwu.edu/~n9343176/old2new.html
> The document goes into excellent detail on the in's and out's of
> building from old tube gear and the possible and useful
> variations of which stages with how much gain go where in the
> amp.
- Build a tube preamp from scratch, and use this to drive another
larger amplifier which does not necessarily have to be tube based. I
have designed things like this, so have others. Good tube sound, and
inexpensive. Really convincing tube distortion, especially if you
add some lowpass filtering to simulate the high frequency cutoff of
guitar speakers.
This is what the Hughes and Kettner Blues Master and Cream Machine
tube preamps did (they've been discontinued). These were entire tube
amplifiers with maybe 2 or 3 watts output, a simulated load, and a
line level output in addition to the speaker output. They did a VERY
respectable job.
10. How can I modify my tube amp to ... ? (also see recommended mods, below)
- get lower hum?
* replace the defective humming tube
* replace or improve the power supply filter capacitors
* fix the defective internal ground wiring, as on a reverb tank, or
previous "improvements" and modifications
* run the preamp filaments on regulated DC, not AC, starting with the
input tubes
* rewire the grounding so the amp is star grounded, and does not use the
chassis as a ground bus
* move the signal wires around, nearer/farther from the chassis or
60 Hz AC carrying wires
* use coax cable in the signal path, at least in the early sections
where noise counts the most. Tie one end of the shield to ground
and terminate the other end with some shrink tube so it cannot
touch anything. This way the coax shield acts as an antenna and
conducts the RF to ground (as well as Faraday shielding hum out).
If you tie both ends to ground you set up some capacitance (and
the possibility of ground loops) you're better off without. The
shield should be tied to the star gound point individually, and
bypassed to the chassis locally with a good RF cap of about 0.001
to 0.01.
George notes "You may already use this in your own amps but I
thought we might share it with the rest of the tinkerers - it's
especially useful for people that are trying to add extra gain
stages. I even use it between the input jacks and the first stage
since in most Fender amps it has to traverse the width of the
board. (Kaschner)
- have higher gain/more distortion?
* install an extra gain stage by
-using an unused tube section if one exists
-adding another tube to the chassis
-using the reverb tubes as additional gain stages
-using a power MOSFET as a cathode follower to drive tone control
and volume controls for lower loss
-using a power MOSFET to replace an existing cathode follower,
freeing up that tube section for more gain
-remove the feedback on the power amp stage; newer Fenders and
other amps use feedback on the power amp to reduce distortion.
Removing this increases gain and and distortion, and makes the
distortion start at lower volumes. On Fenders, it's generally a
white wire from the 'ext speaker' jack to a 2.2k resistor. Cut
this wire, or lift it at one end. To be really slick, put in a
toggle switch. (Edelman)
* use the alternate channel for more gain, perhaps jumpering two
channels together
- have a smoother, less buzzy distortion?
* use a lowpass filter somewhere inside the amp in the signal path
to cut higher harmonics; perhaps a capacitor to ground from the
final preamp tube grid or plate -or-
* use series grid resistors to cut the high frequencies in and after
distortion stages
* use a lowpass filter after the amplifier and before the speakers to
cut out some of the higher overtones.
11. When should I bias my amp and how do I do this?
=================================
A. What is "bias"?
"Bias" in this context refers to the amount of voltage held on the
grids of the output power tubes. This controls the amount of current
the output tube(s) conduct exclusive of the signal current, or,
looking at it another way, the amount of overlap where both tubes are
conducting simultaneously.
I will talk about the output tube current since the terms
"underbiased" and "overbiased" are confusing with tube amps. A
technician who works with only tube amps will usually refer to the
voltage which sets the operating current in the tubes. In these amps,
the bias is a negative voltage, so "overbiased" to such a technician
would mean that the tubes are held in a condition of too little
current, just backwards from the solid state terms most of us are
familiar with. "Underbiased" would mean that the tubes have too
little negative voltage on their grids and are conducting too much
current simultaneously.
The idle current in the output tube and the degree to which the output
tubes overlap in conduction is what you're trying to adjust, not how
many volts go on the grids; you just have to use the grid volts to
change the current and conduction angle.
The whole topic of bias is tied up with the "Operating Class" the
power amp is designed for. There are only three classes useful to us
in tube amps, Classes A, AB1, and AB2. Class A means that the output
tubes are biased so that both tubes are always conducting. Even on
maximum signal peaks, the tube driven most "off" will still be
conducting some current. In both class AB's, the bias is set so that
on a signal peak, one of the tubes can be driven completely off for
some part of a signal cycle. In class AB1, no grid current flows into
the grid of the tube, and in class AB2 some grid current is driven
into the grid of the tubes. There is a class B, where both tubes never
conduct current at the same time, only alternately.
The point of all this is this: The Class of the amplifier is
determined by how much bias current is present. If there is a lot of
bias voltage, the grids are held 'way negative, then only the tube
which is driven by the positive going half wave of the signal at any
moment is conducting. This is class B. It sounds ugly because the
point where the signal crosses over from positive to negative and
begins to drive the other tube is not reproduced cleanly, and creates
[surprise!] crossover distortion. You can look at the output signal
with an oscilloscope and see crossover clearly as you make the bias
voltage too negative for both tubes to conduct at the same time. As
the bias voltage is made less negative and allows both tubes to
conduct a little, the crossover notch diminishes swiftly, and you are
in class AB2; a little less negative, and they both conduct more, and
you have class AB1. If you go further, you get to the point where both
tubes always conduct, making the amp work in class A, which has the
least crossover distortion of any of these operating conditions.
Too little simultaneous conduction in the output devices puts them in
the most nonlinear region of their transfer characteristic, so
crossover distortion is high; but as you increase the amount of
simultaneous conduction, the power used and dissipated by the outputs
goes up, perhaps to a disastrous degree. You are trading standby
current and power dissipation in the output devices off against
distortion. If both outputs are biased almost totally off at idle,
crossover distortion is very bad. As the simultaneous conduction is
increased, crossover goes down rapidly, until it gets smaller than the
residual THD of the amp itself, and becomes much less audible. There
is a fairly broad sweet spot where the crossover distortion is
comparable to the THD and the idle current and idle power dissipation
are reasonably low. This is the region you're looking for.
Lots of bias, both tubes conduct all the time - and eat a lot of
power, get hot, other Class A kinds of things. Little bias, both
tubes overlap less, get less hot, put out more total power - and
produce crossover distortion, which sounds especially unpleasant.
Power tubes individually have slightly different DC gains, so the same
bias voltage on two different tubes produces two different current
levels. "Matched pairs" are two tubes selected to be close together.
Groove Tubes grades tubes from 1 to 10 so that any two "3"'s for
instance are close enough to sub for any other "3", so you don't need
to rebias if you keep buying the same number from them.
> Note that you may not want matched pairs, depending you your taste.
> See section D. below.
> B. When should I bias my amp?
> You should re-bias the amp whenever you change power tubes or modify
> the power amp circuits.
>
> Each power tube needs a certain bias current to keep it operating at
> the point where the amount and type of distortion under normal
> conditions is well controlled. Individual tubes vary widely in the
> grid bias that sets the correct idle bias current. If you change
> tubes or tinker with the circuit, you need to make sure the tubes are
> set back into operation in a way that sounds good and does not cook
> the tubes.
>
> Amps typically provide only one adjustment point for bias, assuming
> that you will have bought matched sets of power tubes.
>
> It is possible to modify your amp to "match" unmatched tubes by
> setting the bias voltage and AC drive level of each tube
> individually. This may require some serious soldering, though. See
> section D. below for a discussion on matching, and the mods section
> for what you have to change.
C. How do I bias my amp?
CAUTION
CAUTION
CAUTION
Keep in mind that tube amps use high voltages, and they can *kill* you
if you don't know what you're doing. So, if in doubt, leave the job
to a qualified technician.
How do you correctly bias an amp? There a few different approaches
but first hook up a speaker or a passive load to the output and remove
any input signals; tube amps need to have a load or they can sometimes
become unstable. Check and make sure the proper size fuse is
installed.
Output Transformer Shunt Method
The most common and simplest procedure is to hook a current meter from
the plate (anode) across half of the primary of the output
transformer; this is called the "output transformer shunt method." The
idea here is that milliammeters commonly have a very low series
impedance so that when placed in parallel to half of the primary,
almost all of the current flows through the ammeter. When you hook
things up this way, your meter is floating at the voltage level of the
plate, which is typically hundreds of volts -- be very careful!
You could open the wire from each plate to the output transformer and
hook in a meter in series with the plate temporarily, but that is a
terrible amount of work for the small gain in accuracy.
Adjust the bias pot so that the current reading is the appropriate
value for the type of tube (see the table below). Let the amp warm up
and note if the bias changes significantly. If so, select a
compromise bias point.
Keep in mind that if your circuit uses more than one tube per side,
the bias current you're reading is multiplied by the number of tubes
(e.g., if you're reading 60 milliamps and there are two power tubes
per side, if the tubes are matched each of the two are getting
nominally 30 milliamps). Check the other side of the circuit to
confirm that the two sides are close (within 5 milliamps) to each
other.
If your ammeter has too high a series impedance, the shunt method
won't work because the bias current gets significantly split between
the meter and the transformer; the meter has no idea how much current
is going through the transformer. You'll know it's not working
because the current values you'll be reading will be much too low no
matter how far you adjust the bias pot, the tubes will be glowing hot,
and when you note that you'll reach quickly for the power switch! If
you don't reach it quickly enough, you might blow a fuse. Don't
despair: you can use another method called the "cathode resistor
method."
Cathode Resistor Method
If the circuit already has a resistor in-line between the cathode and
ground, use it. If the circuit has the cathode hooked up directly to
ground, insert a low value resistor (say 1 Ohm/1 Watt) [even 10 ohms
will work well, as the currents in a tube circuit will cause only a
volt or so max across a 10 ohm resistor, not enough to change the
circuit operation a lot.] in between the cathode and ground. This
doesn't have to be a permanent change to the circuit; you can make a
little adapter that fits between the tube and its socket that runs all
the signals straight through except for the cathode lead -- that path
gets the low value resistor in-line. If you make the adapter, you
don't even have to drop the chassis from the amp to set the bias.
Just pull a tube, install the adpater, and adjust.
Hook up a voltmeter across the resistor and measure the voltage. For
a 1 Ohm resistor, if you read 30 millivolts Ohm's Law says that you
have 30 milliamps running through it. If you have some other value
resistor, make the approriate calculation. Easy! But since the
current at the cathode is the sum of the bias current and some other
leakage currents, you need to compensate the reading a bit, typically
5 to 10 milliamps.
What's nice about the cathode resistor method is that you're not
dealing with high voltages. The cathode sits very close to ground so
the chance of a dangerous mistake is lessened. You're also reading
each tube's bias current individually.
Other Methods
Some of the manufacturers say to set the bias voltage to some
specified voltage, without any other measurements. Presumably some
designer somewhere decided how much was good for you and wrote down
"Set the bias to xx volts" as a good compromise for all the tubes s/he
expected. This method ignores the variability of transconductance in
output tubes, and only gives good results for matched sets that happen
to be exactly like the "typical" ones the designer thought they'd get.
Note that Gr@@ve Tubes tries to help by providing matched tubes with a
bias number from 1 to 10. If you have GT's with a "4" bias number,
and you replace with a GT "4" set, they will have selected only tubes
that are properly biased at that level, and no rebiasing will be
necessary. Of course, GT expects to be repaid a fair profit for this
service to you...
Another way to set bias is to use a test signal, typically a sine
wave. Monitor the output waveform on an oscilloscope and adjust the
bias for minimum crossover distortion. The obvious problem is when
has it "just disappeared"? Most folks do just a bit more than "just
disappeared" and get their outputs too hot causing shortened tube life
and overheating. Not very accurate or repeatable.
You can also use a special purpose instrument that nulls the input
signal out of the output signal so that you can monitor just the
distortion products. You then adjust the bias to get the distortion
to a realistic minimum without making it dramatically less than the
residual THD. This is the premium method, but requires a distortion
analyzer - big bucks.
These methods can be more accurate than the first two methods but they
require expertise and tools that most folks don't have.
If you are a circuit hacker, and live on solder fumes and cold coffee,
you can modify the amp with solid state servo bias adjusters that
twiddle the bias to each output tube on the fly on a continuous, real
time basis to keep each tube -* exactly *- where it ought to be. Only
recommended for real wiring fanatics...
GENERAL BIAS GUIDELINES (from Tremolux@aol.com)
Currents Per Tube - Class AB1 Operation (most musical instrument amps
are designed to run in class AB1)
6L6 - 30 to 35 ma
6V6 - 22 to 27 ma
EL-34/6CA7 - 35 to 40 ma., sometimes even higher!
6550 - 40 to 50 ma
EL-84/6BQ5 - 22 to 27 ma
Class A currents will be higher. Example is 50 ma for a 6L6. Don't
try to run an amp designed for AB1 in pure class A, it will overheat
and probably blow. To handle the higher idle currents, Class A amps
usually run at lower plate voltages.
> D. Matched output tubes - do you need them?
> Do I always have to buy matched pairs of output tubes?
>
> The issue of "matching" ouput tubes, either by buying carefully
> matched pairs or by tweaking the bias levels and drive signals per
> output tube is not a settled one. It used to be common wisdom to
> simply buy matched tubes. A few people noticed, however, that they
> had a favorite pair of output tubes, which made their amp sound much
> better than others. The common assumption was that these tubes were
> better matched somehow. When these tubes get measured, though, it
> usually turns out that they are NOT matched.
>
> The concept of matched output tubes comes to us musical amp types
> from the hifi community, where they are trying to get the lowest
> possible distortion. This was true from the start, when Fender
> was trying to build low distortion amps and copied hifi circuits.
> The concept has simply clung to us, largely through inertia. It is
> relatively well accepted even in the hifi circles now that
> even-order distortion is euphonic, sounds good to our ears. It is
> very likely that the even-order distortion produced when mismatched
> output tubes are used sounds better than perfectly matched tubes.
>
> Note that the commercial tube suppliers have good reason for wanting
> to sell us matched sets at a premium. I would expect their opinion
> to be that matched sets are absolutely crucial. As in all musical
> matters, let your own personal ears be your guide.
>
> If you have a set of tubes you know are not matched, or if you have
> modified your amp to be able to set the bias and drive levels on
> each output tube separately so you can either match or not match
> the tubes at will, you might want to try un-matching them and
> see how it sounds to you.
12. Amplifier Modifications
A. Recommended amp modifications
- put a fuse in the B+ line after the rectifier(s) and before the first
capacitor filter. This can save burning out your power transformer and
maybe your output transformer if you get a shorted filter cap, shorted
output tube, or lose bias on an output tube. It -* might *- save an
output tube that has lost bias even though it also might not.
> The fuse current rating should be slightly larger than the max current
> rating for your output tubes, generally much less than 1A.
- put a 130 or 150 Volt MOV surge protector across the AC line at the
power transformer primary to absorb spikes from air conditioners and
motors turning on and punching through the primary insulation.
Recent articles say that 130V MOV's will eventually short, recommending
only 150V MOV's.
- get rid of all two wire line cords and line switching arrangements.
Refit with three wire cords, tieing the safety ground to the chassis.
You'll love this the next time you touch a mike or stand while holding
a guitar. No shocks. Oh, yeah. Do it to ALL your equipment to be safe.
- consider putting a small fan in your amp to cool it. Try a 240vac fan
running from the 120 vac line supply, which will run much slower and
quieter than a 120vac one.
- install small cathode resistors and independent bias adjustment for
each output tube to make biasing easy.
- open the feedback from the power amp output to it's input for more
power amp gain, more and earlier distortion. Or better yet, put in
a spst switch and you can pick the characteristics on the fly...
- for the adventurous, add a separate filament transformer/rectifier/
filter capacitor to make 9-12VDC at several amps and then use a
three terminal rectifier to regulate this down to 6.3VDC, and feed
this to your preamp tube filaments. Hum from filaments will drop
right through the floor. Lotsa work, though.
> - put 1500Volt, 1A silicon diodes in series with the two sections of
> your rectifier tube (if you have a rectifier tube) so that if the
> rectifier tube shorts, the silicon will save the output tubes, and
> power and output transformer.
> B. OK but complex, difficult or involved modifications
> ***** THESE ARE FOR TECHNICALLY ADVANTAGED FOLKS ONLY ****
> - remove the single bias adjust pot in your amp and put in two,
> connecting one to each output tube. You can now set the bias
> voltage on each tube to be different, which can match the DC
> currents for un-matched tubes, or un-match matched ones for
> more even harmonic distortion.
> - tinker the driver circuit to let you adjust the relative amount
> of AC drive to each output tube. This lets you match/unmatch
> output tubes in an AC sense just like the bias mod lets you change
> the relative DC points.
C. NOT Recommended amp modifications
These are likely to be just plain bad, either grossly (it dies soon)
or subtly (it dies slowly, eats tubes, or other sicknesses).
- using a variac to run it at a higher or lower line voltage. This
might be OK except that running it higher can overdissipate parts
and burn them up or overvoltage things like filter caps, which can
short and burn out your -* expensive *- output transformers, as well
as burning out your tube filaments by putting too much current
through them; and running it lower starves the filaments for
current, so they can't put out enough electrons, and any remaining
gas in the tube bombards the cathodes, poisoning the electron
emitting materials on the cathode surface, and wearing the tubes out
early.
- adding massive amounts of capacitance to the power supply filters to
reduce hum. Probably OK with solid state rectifiers, but in amps
with tube rectifiers this can cause current spikes in the rectifiers
that exceed the instantaneous current rating of the rectifier and
wear it out quickly.
Nathan points out "I seem to recall one of my Tube Amp Mentors
telling me that this is pretty much only the case with the first
filter cap after the rectifier, and that the impeadance of the power
supply was high enough that you could dump hundreds of uf worth of
filtering on latter stages (though the only place it's of much
benefit is at the power tube plate supply point.)
13. Tube Characteristics and substitutions
Under construction. To contain quick and dirty subs and some tube data
such as recommended bias current and appx voltages. These subs are all
taken from the Tube Substitution Handbook sold by Antique Electronics
Supply.
A (short) catalog of tubes you are likely to see in a guitar amp:
12AX7[A, WA] and substitutes - preamp and driver tubes
12AT7, 12AU7 and subs, preamp and driver tubes
12AY7 - driver tubes
6EU7 - dual triode used in some older amps for preamp tube
6L6 types - power output tubes, up to 50 watts/pair, a mainstay of Fender
EL34 - Euro power pentodes, up to 50 watts/pair, many Marshalls
6V6 - smaller, lower power cousin of the 6L6, 10-14 watts per pair; used
in smaller Fenders
EL84 - fits a 9 pin socket like a 12AX7 but twice as tall; miniature
power pentode, good for 12-18 watts per pair; used in smaller Vox
amps, and a quad of these drives the Vox AC-30 for 30 watts.
Substitutions:
* means appropriate for parallel filament circuits
# means may not work in all circuits
Preamp and driver tube substitutions:
12AX7 (high gain dual triodes with pinout 9A)
12AD7* 12DT7 7729
12AU7# 5751* B339
12AU7A# 5751WA* B759
12AX7 6057 CV4004
12AX7A 6681 E83CC
12AX7WA 6L13 ECC803
12BZ7* 7025 ECC83
12DF7 7025A M8137
12DM7* 7494
12AU7 (moderately high gain dual triodes with pinout 9A)
12AU7[A,AW,] 6189 7730
12AX7* and subs 6670 ECC186
5814[A,AW]* 6680 ECC802
5963 7316 ECC82
6067 7489 M8136
12AT7 (medium gain dual triodes with pinout 9A)
12AT7[many suffixes] 7492 E81CC
6201 7728 ECC801
6679 A2900 M8162
ECC81 B152 QA2406
12AZ7[A]* B309 QB309
6060 B739
6671 CV4024
12AY7 (low gain dual triodes with pinout 9A)
12AY7(and suffixes) 6072
2082
Power tube substitutions:
6BQ5/EL84 (miniature pentode with pinout 9CV)
6267 7189 EF86
6BQ5 7189A EL84
6BQ5WA 7320 N709
6P15 E84L Z729
6L6 (beam power tube with pinout 7AC)
6L6(many suffixes) 7581(A)
5881 WT6
5932 EL37
EL34/6CA7 (power pentode with pinout 8ET)
EL34 12E13
6CA7 KT77
7D11 KT88
6550 (power pentode with pinout 7S)
6550[A] 7027A#
7D11 KT88
12E13
Cautionary Tubes - these are very hard to find
7591/7591A - legend has it that these otherwise excellent tubes
were all bought up by an oriental buyer who toured the USA
paying cash for all of them he could find, then disappearing.
You are likely to only find used ones or the odd pair in some
out of the way place. Dealers will in general not have them.
These were used a lot in old Ampegs. They are very small and
high gain for their physical size, so there may not be a lot of
room in a chassis for a larger replacement. The 5881 will work
in some circuits, but has significantly lower transconductance.
> Rumor Update: The rumor mill on the net says that the Russians
> will soon be making 7591's soon. Cross your fingers...
7199 - combination pentode/triode used as a one-tube voltage amp/phase
inverter/driver for a pair of output tubes in some Ampeg amplifiers
Note: These were once popular, but are now getting rarer and more
expensive. There are a number of other pentode/triodes that can be
substituted, but the pinouts are different and this will require
require rewiring the socket for the tube. Examples are the 6AN8 and
the 6U8. There is a Russian tube that is labeled 7199 which may
work, although this is new.
7027/7027A - this is a high power tube similar to a 6550. The supply
of these is very poor.
7189/7189A - a higher power/voltage version of the 6BQ5/EL84. Hard
to find. A stock 6BQ5/EL84 may work if the power and voltage
conditions in the amp are not right out at the limits of the tube
design.
14. Maintenance (Still under construction)
Lots of good info from Jack Darr's Electric Guitar Repair Book and
The Tube Amp Book. Look for:
- retensioning tube socket contacts
- carbonized arc paths
- checking for capacitor leakage
> From watching a tech work on Fenders, I picked up a nice tidbit.
> The eyelet boards in Fenders have most components mounted across
> the eyelet board. A very few parts run along the length of the
> eyelet board. Because the eyelet board flexes, there is a lot of
> stress on the solder joints at the end of these lengthwise
> components and the joints often crack. Every time you open up a
> Fender, take a look and maybe a soldering iron to these joints. If
> it's your personal amp, you might want to get a new part for these
> positions with long leads and bend a loop in the leads so that the
> leads can flex and not put stress on the solder joints.
Appendix A. Tube Stuff Suppliers
The following article appeared in rec.radio.swap. A lot of this may be
more oriented to radio than audio, but there is a large cross over in
many tube types, as well as in the power transformers and power supply
components.
======================================================================
Gang: The enclosed is a bit long but it's the most complete list
of tube sellers I've seen presented on the internet. You'll want to send
this list to your printer! I didn't edit it down like I usually do
since that would have made it quit difficult to read. // Jeff NH6IL
*****************************************************************
Article: 18193 of rec.radio.swap
From: brian.carling@acenet.com (Brian Carling)
List of suppliers and sources for finding vacuum tubes:
Adkins:Charles P. N8QXP (313) 382-0272
1821 La Blanc.
Lincoln Park,MI 48146 Tubes
Allied Electronics: 800-433-5700 Located in 36 states, 83 branches.
7410 Pebble Drive Call for nearest branch. Call for Catalog.
Fort Worth, Tx. 76118: Electronic components and tubes. Min.Prepaid
order $25. Min. Credit Card order $50 as well as COD is $50. Min.
Antique Audio 512-467-0304
5555 N. Lamar, Bldg. H-105
Austin, TX 78751 Tubes, parts, books, kits
Antique Electronic Supply Co. 602-820-5411
6221 S. Maple Avenue
Tempe, AZ 85283 (Tubes & other components)
Antique Radio Classified 508-371-0512 Write for free sample.
P.O. Box 802 Magazine. You'll find almost ANYTHING here
Carlisle, MA 01741 for older radios, obscure parts, tubes etc.
Arlen Supply Company (610) 352-9311 / -9388 = FAX
7409 W. Chester Pike
Upper Darby, PA 19082 Tubes. 1 million stocked. Minimum $150.00!
A.R.S. 602-820-5411
Arizona Need address Tubes
David Ask No phone number given
RR 2
Houston, MN 55943 Tubes 4, 5 and 6 pin tubes. Send $1 for list
Mel Brooks, K5DJB No phone number given
932 Macklyn Lane
Bartlesville, OK 74006 Tubes, parts, schematics (incl. antique)
Bauman:Jeff, WB5KZW. 313-435-9922: 313-661-0202 Jeff had 1500 Tubes
6647 Stonebridge East, for sale as of December,1993
West Bloomfield, MI 48322
Cable:John, 619-258-7931
Address needed. Tubes from 1941 to 1960, new.
CeCo Communications. 800-221-0860: 212-646-6300
2115 Avenue X Vacuum tubes
Brooklyn, NY 11235
C & N Electronics 800-421-9397: 612-429-9397
6104 Egg Lake Road FAX 612-429-0292
Hugo, MN 55038 Buy & sell tubes
Daily Electronics 800-346-6667: 206-896-8856: FAX 206-896-5476
10914 N.E. 39th Street
Vancouver, WA 98682 Tubes, all types.
Davilyn Corp. 800-235-6222 xct.CA: 818-787-3334 CA: FAX 818-787-4732
13406 Saticoy St. Electronic Tubes. Good Prices, Call for Catalog
North Hollywood, CA 91605-3475 Also Surplus Electronic Gear.
DH Distributors 316-684-0050
P.O. Box 48623
Wichita, KS 67201 Tubes, radio, TV, industrial
Electron Tube Enterprises 802-879-0611
Box 311
Essex, VT 05451 Tubes
Electronic Bits 'N Pieces 303-361-6530
P.O. Box 31654
Aurora, CO 80041 Tubes, transistors, diodes, chips
William Erickson, W4UIL No phone number given
3905 Cherrywood Lane
Annandale, VA 22003-1901 Tubes, older radios etc.
E.S.R.C. (407) 735-3397
P.O. Box 1192
Delray Beach, FL 33447-1192 Buy, sell, swap tubes of all kinds
Fair Radio Sales. 419-227-6573:419-223-2196: FAX 419-227-1313
1016 E. Eureka Box 1105 Parts, transformers, power supplies,
Lima, OH 45802 Surplus and gov't surplus radios etc.
Fala Electronics (No number listed) send S.A.S.E.
P.O. Box 1376-1
Milwaukee, WI 53201 Vacuum tubes
Melvin Heineken, K5MNJ No phone number given
2204 Spruce Needle Rd. N.E.
Rio Rancho, NM 87124-6308 Tubes. New unboxed. Other parts.
Henry Radio Co. (310) 820-1234
2050 S. Bundy Drive
Los Angeles, CA 90025 New tubes
International Components Corp.800-325-0101: FAX 503-336-4400
1803 NW Lincoln Way Cabinets, components & vacuum tubes
Toledo, OR 97391
Jolida Tube Factory 800-783-2555
10820 Guilford Road Vacuum tubes
Annapolis Junction, MD 20701
KB5QOH (No name given) No phone number given
667 Nine Mile Hill Road
Fairbanks, AK 99712 Tubes, parts, used amateur gear
Kirby No number listed
298 W. Carmel Drive Tubes, new up to 90% off
Carmel, IN 46032
Cliff Kurtz, N6ZU No phone number given
6727 N. Pershing Avenue
Stockton, CA 95207-2522 Tubes. Minimum order $10.00
Robert Lang AA2EO (212) 877-0980
120 W. 70th Street Apt. 7-A
New York, NY 10023 Tubes, vacuum variables, xfmrs etc.
Madison Electronics (800) 231-3057
12310 Zavalla
Houston, TX 77085 Tubes, meters etc.
Rex Mason (704) 392-0359
100 Honeywood Avenue
Charlotte, NC 28216 Tubes, antique parts, amateur, TV, VCR
New Sensor Corp. 800-633-5477: 212-529-0466: FAX 212-529-0486
133 Fifth Avenue. Vacuum tubes galore! Call for list.Min.Order $50.
New York, NY 10003 Std. test= $0.75/Tube. Premium Match $2/Tube
No name (SHY?!) No phone number given
5150 Merritt Road
Black Hawk, SD 57718 Tubes. S.A.S.E. for list
P.E.M. Tubes (916) 383-9107
7392 French Road Tubes, radio, TV, transmitting, CRT
Sacramento, CA 95828
Pride Tubes 800-638-3925: 205-650-5522: FAX 205-880-8077
8200 South Memorial Parkway (800) 456-5642 100% RF Tested Tubes
Huntsville, AL. 35802
Rauchwerger, Lawrence 217-352-6195
1610 1/2, W. Union St
Champaign, IL 61821 Tubes. S.A.S.E. list
R.F Parts. To Order 800-737-2787:619-744-0700 or 0750 for Tech info
1320 Grand Avenue FAX 619-744-1943
San Marcos, CA 92069 Diamond Antennas, RF Power Transistors & Tubes.
Richardson Electronics (708) 208-2200 / (800) 235-2143
40 W. 267 Keflinger Road
La Fox, IL 60147 Tubes, RF parts
Steinmetz Electronics 219-931-9316
7519 Maplewood Avenue Tubes
Hammond, IN 46324
Svetlana Electron Devices Co. (415) 233-0429 / - 0439 = FAX
3000 Alpine Road
Portola Valley, CA 94028 Tubes, RF power etc.
Turner Electronics No number listed
16701 Main Street Suite 121
Hesperia, CA 92345 Tubes, capacitors, S.A.S.E. list
Unity Electronics No number listed
P.O. Box 213 Vacuum tubes
Elizabeth, NJ 07206
C. Verderber No phone number given
2266, Route 9G
Rhinebeck, NY 12572 Radios & tubes
Carl R. Warren, W0KWS (417) 869-4738
MPO Box 567
Springfield, MO 65801 Tubes & parts. Also repair service
Wayne (no last name given) (301) 963-4619
No address given
Gaithersburg, MD Tubes, equipment, parts, books
Westgate Co. (800) 213-4563
Need address! Tubes & transistors
This list was prepared by AF4K, Brian Carling
Please send additional sources for inclusion in this list.
If you go to a hamfest and see someone selling tubes, get a card
please and send me their name, address and phone number.
AF4K @ W3INK
(301) 990-6070
brian.carling@acenet.com
Appendix B. Tube Makers Producing Today (Eric Barbour news posting)
(The following is the text of a note posted to the alt.guitar news
group by Eric Barbour )
1. Different makers of tubes use different designs. There are six
makers of common audio tubes right now:
Shuguang, China--good 12AX7s, so-so power tubes
Tesla, Czech--ok EL34s, preamp tubes variable
Reflector, Russia (sold under Sovtek brand)--good 5881, EL84, so-so 12AX7
(they came out with EL34s recently---I am testing them)
Kaluga, Russia (only a few types--sold under Sovtek, Audio Glassic)
good 5881s, not sure what else they make today
Svetlana, Russia--has a 6550 now, good---will introduce an EL34 soon
EI, Yugoslavia (in Serbia)--fair 12AX7s, fair EL34s,
future supplies are questionable because Serbian products are under
economic sanction; thanks to that Bosnia business!
That's ALL there are right now. That's it. Any NEW tube you buy is
from one of the above.
For your guitar amp, I would recommend the "Sovtek" 5881, it's a
really nice, rugged and smooth-sounding tube. It was a military type
used in servo amps in jet aircraft, so it has to be good. If you have
a Marshall or other EL34 amp, the Sovtek 6CA7 imitation (recently
released) is probably most rugged. If you want more distortion and a
more bluesy sound, you want the skinny EL34s. The Svetlana EL34 will
be a skinny type, it should be very good.