Here's a list of some of the most common technical
questions we get asked and their answers. We've also included
some Internet links to help out.
Power Tubes and Bias
Preamp Tubes
Reverb
Tremolo and Vibrato
Hum
Schematics and More Amp Info
Power Tubes and Bias
Do I need to bias my new power tubes or
can I just plug them in and go?
In the best of worlds you would have a qualified
tech install your tubes, check your bias and adjust for
best tube performance and longevity. In a good portion of
vintage Ampeg amps such as the Gemini I, the power tubes
are "cathode biased" and are self biasing. It
doesn't hurt to still check the current draw on these amps
but unless the new tubes are way out of whack (pretty rare)
you can just plug them in and go. Most other amps, Ampeg
V4, Fender Twin etc. use a fixed bias system. The bias is
set at the factory on these amps to run their particular
type of power tube so generally speaking. you should be
able to plug the right tube type in and go. But, it is common
for these factory set bias supplies to drift so it is best
to have it checked and set up by a good tech. Your tubes
glow when they are on from the filament, the part that heats
up the tube components. But an easy way to tell if your
tubes are in trouble is if the plates, the gray metal on
the outermost part of the tube glows a bright red. This
indicates an "under biased" situation in which
the tubes are literally being fried! It's easier to see
in a darkened room. Bottom line we recommend having your
power tubes installed by a qualified tech to save yourself
any potential headaches and for best results out of your new
tubes.
Are the 7027A, 7591A and 7868 power tubes
used in vintage Ampeg amps available?
Thankfully there are two companies making
7027/7027A power tubes. Electro-Harmonix has been making
the 7591A for a couple of years now and we've been very
pleased with them. For now no one is offering the 7868 although
I've been told it's in the works from Electro-Harmonix.
Otherwise you will need to modify your amp with new 8 pin
tube sockets. These will allow you to use other more common
tubes such as the 6L6 with a few other alterations to the
circuit.
Preamp Tubes
What about those weird preamp tubes in
Ampegs, 12DW7, 6CG7, 6BK11 etc..?
A good portion of these tubes are in current
production, 12DW7, 12BH7, 6CG7 etc.
However the Compactron type tube are not and
probably will never be made again. This includes: 6BK11,
6K11, 6U10 etc. Hold onto your old ones for backup. Good
news is they tend to last a long time in the circuit. There
are currently new old stock available on these and there
are some substitutions that can be made. Just keep in mind
that these will eventually disappear.
Reverb
What caused my reverb to stop working?
Here's a short list of things that can cause
reverb problems.
- A bad reverb tank
- Weak driver and recovery preamp tubes,
In Ampeg Type "C" systems this is usually the
6CG7 tube and a 12AX7.
- Bad tank cables
- Bad footswitch
- A bad reverb transformer as used in Fenders
Tremolo and Vibrato
Why doesn't my tremolo/vibrato work?
Here's a short list of things that cause tremolo/vibrato
failure.
- Bad or weak Tremolo or Vibrato Units. Causes
weak trem/vib in vintage Ampegs
- and can cause volume loss when trem. is
turned up.
- Bad or weak capacitors in trem/vib circuit.
- Weak tubes in trem/vib circuit.
- Bad footswitch.
Hum
My amp has a low end hum no matter what
volume I play, why?
Most likely your amp could use a "cap
job". The filter capacitors in your power supply are
weak and failing. You may also have a bad power tube, rectifier
tube, diode, or power transformer. Remember -- on a lot
of Ampegs and other vintage amps there is a hum balance
control. Try adjusting that first to see if you can remove
the hum. Sometimes this control goes bad too. Otherwise
have a tech check these other items to effect repair.
Schematics and More Amp Info
Ampeg Schematics available on the web.
The
Unofficial Ampeg Site.
The Tube Amp Book by Aspen Pittman.
Most comprehensive collection of schematics available.
Other Vintage Amp Site Links:
Tone
Mod for Vintage Ampegs. We're not big on doing mods
not originally done at the factory but these seemed useful
and it is based on an 70's Ampeg update to the original
B15N circuit.
Ampeg
Auctions on 
This
is a continually updating link that will show all the Ampeg
parts and amps for sale on Ebay.
The
Ampeg Scroll Bass Page: An amazing tribute to the Scroll
Bass by Bruce Johnson. He manufactures and sells the beautiful
reissues too! Stuffed full of history and info.
Ampeg
Schematics Online Courtesy of Joe Piaza's Backstage Amplification
Page: Joe has put alot of time and effort into making
available Ampeg schematics, voltage charts and tube data.
Gear Head LInks:
Gear Heads Unite!: cool links to other vintage amp lines.
The
Sunn Shack: Get all the glorious details on these powerhouse
amps.
The Univox
Page: Another great amp company from the vintage era.
This site contains a very comprehensive listing of info,
pictures schematics and more.
Traynor
Amplifiers: Velvet Black website. Great site for the
legendary Canadian amps.
Garnet
Amps: Another legendary Canadian amp as used by the
Guess Who.
Feeling overwhelmed? Don't want to deal
with it? We offer a full line of electronic, speaker and
cabinet repairs. See our Services page for more details.
