Reprinted from Guitar World
Tube Amplifier Care and Hygiene
by Csar Diaz and Daniel Jacoubovitch
Like teeth, amplifiers are a lot less
exciting to routinely clean and care for than they are to repair in an emergency.
Not that amps need daily flossing and brushing, but they do get gummed
up with use. If the crud they pick up over time isn't cleaned off occasionally,
they'll develop serious problems requiring professional care.
Many of the irritating, sound-robbing problems that plague older tube
amplifiers can be traced to dirt and oxidation that have accumulated on contact surfaces
over the years. Dirt and oxidation deposits in tube sockets and amplifier controls
cause unwanted distortion, loss of volume and a wide range of crackling and popping
The vintage Fender, Magnatone, Ampeg and other tube amplifiers that
have come to be prized by rock and roll players have all seen enough use and age to suffer
from these symptoms.
Just because an amp says Fender on the front and is covered in tweed
doesn't mean it will put out the sweet, singing tones that you expect from it.
During the years that fifties and sixties tube amplifiers have been picking up value and a
cult following, most of them have also been picking up sound- and power- robbing dirt and
Airborne dust that settles in amplifiers is conductive and
electrostatically charged. Dust deposits interfere with signal transfer between
components, causing stray noises, distortion, and generally dissatisfying amplifier
performance. The dust's electrostatic charge attracts more airborne dust, causing
more interference with the amp's circuitry, further hastening amp failure.
Oxidation deposits on amplifier-control and tube-socket contact
surfaces also impede signal transfer, causing unsatisfactory amp performance. Sewing
machine and 3-in-1 oil foolishly squirted into amp controls fouls the components and
attracts more sound-robbing dirt. The more conductive contaminants settle on
amplifier surfaces, the higher the risk of arcing – current taking a
component-destroying jump between normally unconnected electrodes.
In the worst case, dirt and oxidation can combine with moisture
to cause the big "C" – catastrophic failure: the destruction of
multiple components due to arcing and consequent short-circuiting across a large surface
of amp circuitry. In the usual -less drastic-case, dirt and oxidation rob an
amplifier of power and clarity.
A simple amp tune-up requiring only a few tools and supplies can clean
up the sound of any older tube amp considerably. The tune-up is part of the
maintenance routine that a good service shop will do as part of most repair jobs.
Many amps brought in for repair only need this basic tune-up, and perhaps a tube or so, to
get back into service.
Doing the job at home will avoid needless service expenses by
eliminating the common causes of poor amplifier performance. When the amp does need
to go to the shop, having it clean will save you from paying for the bench time it would
otherwise take to get that part of the job done. Also, from the repairman's point of
view it's no fun to have to go wading through someone's audio toilet bowl –
dust, grease, rust and beer that leaked in and crystallized on the chassis and circuitry
– looking for a failed component.
After the amp is cleaned up, some attention to how it's stored and
used will protect it from dirt and oxidation build-up, and keep it working and sounding
It's a good idea to let your amp sit unused for a couple of days
before the tune-up. This will give the filter capacitors some time to lose their
charge and you a chance to round up supplies for the job.
Letting the capacitors discharge slowly is preferable to having them
do it all at once through your body while you're poking around inside the amp.
Having the supplies you need on hand makes the job go faster; you'll want screwdrivers,
some contact cleaner (Csar uses Gunk brand choke & carburetor cleaner and WD-40), a
toothbrush and – unless you own an air compressor – an aerosol can of
compressed air. If you know how to use them, soldering supplies and a volt/ohm meter
can also come in handy – but aren't essential.
Start by unplugging the amp from the wall, the speakers from the amp,
and removing the amp chassis from the case. For Fender amps, removing the chassis
involves unscrewing the upper back case panel, then unscrewing the chassis from the top of
the case. Put the screws, nuts, and lockwashers where they won't get lost.
With the chassis out of the case, you can locate the filter capacitors
you'll want to avoid touching as you perform the tune-up. These will be cardboard
cylinders (usually orange or tan or vintage Fenders) with "+" printed near one
terminal. It's also a good idea to steer clear of wiring connected to the power
transformer (that's the large, heavy one); it's a discharge path for the filter
If you haven't given the capacitors a couple of days to discharge
– or if you just want to be cautious – you can use a short length of
insulated wire with alligator clips on the ends to discharge them. First, make
certain that the amp is unplugged. Attach one alligator clip to a capacitor's
positive (+) lead, then touch the other clip to the amp chassis several times.
Repeat the procedure for each capacitor marked with a voltage (VDC) rating higher than
25. The time spent on this precaution can spare you from a numbing electric shock
that you'll remember long after the amp is back together.
Now that the coast is clear, you can proceed with the tune-up.
Start by cleaning dust and dirt off of chassis, component, and connection surfaces.
Use compressed air to blow loose dirt away. For dust stuck to component and chassis
surfaces, Csar works with a toothbrush in one hand and a can of compressed air.
Don't waste time on crud that's leaked out of dead capacitors; it's there to stay.
As you clean off solder joints, examine each connection carefully to
see if the wire is solidly joined to its terminal. Wires that wiggle loosely from
their connections and solder joints showing visible breaks can degrade your sound. If you
have a volt/ohm meter and soldering supplies, this part of the operation is a good time
for checking circuit continuity and desoldering and resoldering worn connections.
Tighten down the power transformer screws. On tweed Fender
amps, the only way that the transformers are grounded is through their mounting
screws. A poorly grounded transformer can cause intermittence in the amp's
output. You may need to substitute mounting screws one size larger than the old ones
to restore a good connection between transformer and chassis.
With the underbrush cleared, you can start work on the tube sockets and tone
and volume controls – areas particularly sensitive to interference from dirt and
oxidation. You'll be using solvents and friction to clean contact surfaces.
The cleaner you get and keep these surfaces, the louder and clearer your amp will sound.
Clean one tube socket at a time. Take out the tube, spray
contact cleaner – or Gunk followed by WD-40 – into the socket, then
re-insert it and shake it around in the socket to expose clean contact surface. Be
careful with the spray, the idea is to use enough to clean the part you're working on,
without saturating the surrounding area. If the socket was particularly dirty,
repeat the procedure before moving on to the next one.
Clean the tone and volume controls – potentiometers, or
"pots", for short – by spraying contract cleaner through the openings
in their covers. Spray in a little cleaner, turn the shaft briskly back and forth a
few times, then flush with another shot of cleaner. If you're using Gunk, flush with
WD-40 right after you spray the carburetor cleaner; leaving Gunk on too long can
freeze the control shaft.
Re-mount the amplifier in the case and reconnect the speaker.
Now that your tube sockets and pots are clean, you can troubleshoot your tubesa
– another potential source of stray noise, distortion, and weakened sound.
All tube amplifiers have at least one power tube (such as 6L6,
6V6, or 5881), and at least one preamplifier tube (such as 12AX7 or 7025). Most
older amps will also have one rectifier tube (such as 5Y3GT, 5U4, or GZ34).
Drugstore tube testers can be used to tell if tubes are dead or
alive, but they don't tell you anything about whether a live tube is causing sound
problems. Tube problems that won't show up on a standard tube tester can be
diagnosed in the amp.
With all the tubes in their sockets, the tube covers off, and
nothing plugged into the amp inputs, turn the power on and crank all the controls up to
Troubleshooting rectifier tubes is easy; they're either dead or
alive. If the rectifier tube lights up when you turn the amp on, it works.
A power tube that doesn't light up is dead for sure. A
healthy power tube will light up and give off a medium-intensity orange glow. Don't
worry about power tubes that give off a dull blue glow; they don't necessarily need
replacement unless they have other problems.
Power tubes that glow bright red, however, are a sign of
trouble. Try another power tube of the correct value in the socket. If the new
tube still glows bright red, there is probably a failed component in the circuitry to that
tube, and you should take your amp to a professional to get the problem tracked down and
Tap each power tube with our fingernail, tubes that send a loud,
low-frequency noise through the speaker when they're tapped should be replaced.
Inspect the shaft on the base of each rectifier and power tube to
make certain that its guide pin – the ridge that slides into a groove in the
socket's center hole, aligning the tube pins with their proper socket connections
– is intact. Incorrectly inserted tubes due to broken guide pins are
probably the single most common cause of amplifier failure.
Use your fingernail to tap each preamp tube. If the tapping
is amplified and comes out of the speaker as a loud, high-frequency noise, the tube is
causing problems. If there's another socket that takes the same value tube, try the
questionable tube in that socket. Because of differences in circuitry leading to
sockets that use identical tubes, a tube that makes noise in one socket can work just fine
in another. If the tube causes problems in all the sockets you try, you'll need to
replace it with a new one.
You can now check out the amp's speaker(s) as the last operation
in your tune-up. Plug in your guitar and set the amplifier to a low volume;
you won't be able to tell the difference between amplifier and speaker distortion at high
volume. Slowly play a few full chords. If the speaker sounds distorted or
gravelly it may need repair. Try the amp through another speaker (one you know is
working right). If the problem goes away, go ahead and get the first speaker
Now that you've rid your amp of dirt and oxidation and
substituted or replaced problem tubes, it should sound clearer, louder, and generally
healthier than it did before the tune-up. a clean amp is a happy amp.
There are precautions you can take to keep it clean and
happy. Protect it from dust by keeping it covered when it isn't in use. You
can slow down oxidation build-up by keeping the amp away from damp places and protecting
it from rapid temperature changes. These changes cause condensation inside the amp,
depositing moisture on components and connections. The moisture is particularly
harmful to components that are made with paper or cardboard – capacitors and
transformers – weakening them and hastening component failure. The
moisture also cause oxidation, fouling the tube sockets and controls you've just finished
Never power up a cold amplifier; let it come up to room
temperature before you turn it on. Sudden heating can crack cold power tubes.
Cold air inside the chassis condenses as the amp warms up, depositing moisture on
component surfaces that can cause arcing and component failures.
Don't keep the amp anywhere you wouldn't be comfortable
sleeping. Unless you're a lot weirder than most vintage amp owners, this means
you'll never leave your amp in a car trunk overnight or store it in a damp basement.
Semi-annual tune-ups and regular attention to how you use and store
your amplifier will keep it sounding sweet and strong – and save you the pain
and expense of avoidable breakdowns.