T ECHVIEWS
Tube Amp Tune-Up
Just like your car will eventually sputter to
a halt and die if you never change the oil,
your amp will eventually develop problems
if you neglect to devote some time to maintenance. It’s a lot better to “change the oil”
in your equipment during those rare pockets
of downtime than it is to be standing in front
of an audience with a dead amp. Let’s take
a look at a few things you can do to tune-up
your gear.
Tubes
This one almost goes without saying, but it’s
surprising how many people fail to remember
it: the best time to get fresh, good sounding
tubes is before you need them. If there is a
spare set of tubes that you’ve already tested
in your amp and know work fine, you can
simply replace a dead one, even on stage or
between sets. As an added bonus, you’ll pay
less for your tubes this way, because you’ll
have time to hunt for good deals.
Fuses
Fuses can wear out. Heat from current pulses
causes the element to flex slightly, eventually
developing thin spots and breaking. How
soon this will happen depends on how close
to the normal blowing current it carries. It
could be months or it could be centuries.
Rather than take a chance, it makes sense to
put in a new one every few years. You can
keep the old one for a known-good spare, or
better yet, get a fresh box of five to keep in
your gig bag.
Socket Contacts
Your tube sockets get hot. Over time, a
layer of corrosion will eventually develop on
the contacts. Bad contacts make for erratic
sound – strange crackling noises and dropouts. The fix is to clean the tube socket contacts and tube pins.
Cleaning your tube pins is simple enough;
rub a Scotch-Brite cleaning pad on the pins
just enough to make them shiny again. Leave
the tubes out of your amp for the socket
cleaning steps. Cleaning your socket contacts
will require a little more caution. I’ve spelled
it out for you below, but if you can’t follow
safety instructions, don’t try this – have
your tech do it for you.
1. Unplug your amp and leave it off and
unplugged for a least one ( 1) hour.
4 PREMIERGUITAR FEBRUARY 2008
2. Use that hour to obtain electronic contact
cleaner, pipe cleaners and wooden dowels,
wooden or plastic chopsticks or bamboo barbecue skewers.
3. Wind a pipe cleaner around one end of
your wooden stick, leaving about 1” of the
pipe cleaner extending from the end of the
stick. Wind some tape over the pipe cleaner
on the stick to hold it down firmly.
4. Hold the wooden stick at least 1” from
the pipe cleaner. Do not touch the pipe
cleaner while you are scrubbing! This is
important for your safety; if you can’t be sure
you will not touch the pipe cleaner while
doing this, get a tech to clean your sockets
for you.
5. Saturate the free length of the pipe cleaner with cleaning solution and stick it into the
opening in the tube socket. Scrub the pipe
cleaner in and out of the opening, cleaning
the inside of the contact pin. Repeat this for
every tube socket hole.
Loose Nuts
The sound from your amp can loosen any
fastener over time. Spend some of your
tune-up time inspecting your amp and
tightening things back down. Amps can also
sometimes develop a hum not related to the
litany of normal hum-inducing causes, and
in some cases can start picking up radio stations. When the bushings of the controls and
jacks no longer make good contact with the
chassis, hum and RF signals can creep in. So,
if you’re not in the mood for NPR, tighten
them up. Use a socket wrench to fit over the
end of your jacks and tighten the nut on the
jack firmly. Remove your amp’s knobs and do
the same for the controls. Jacks with a plastic
bushing do not cause hum if loose, but it
still makes sense to make sure they’re tight
enough not to rotate and break the attached
wires. Don’t over-tighten; just make sure
they’re nicely snug with the chassis.
Do the amplifier safety dance again by leaving it unplugged for an hour before opening
the back up and retightening the nuts that
secure your speakers. There is no need to
crank the nuts until the speaker bends – just
make sure they are tight. Do the same for
the handle fixing bolts and nuts, and the
screws that hold the chassis. For your own
safety, avoid touching anything inside the
electronics chassis.
In the process of your tune-up, you may find
things that really need looked at by a tech.
Make a list and haul it down to the shop.
Just like tubes, the best time to have an amp
in with the doctor is when its not sick!
R.G. Keen
Chief Engineer
Visual Sound
visualsound.net
