Hi Jeff,
I get Premier Guitar in the mail every
month, and after a quick flip through the
magazine to see what’s in store, I turn to
your amp column. I’m writing today hoping
you can help me with a problem, as I
have no idea what’s wrong.
My problem is with my ’59 Bassman reissue.
I was using it at a gig last weekend,
when it began to crackle every now and
then. It wasn’t a speaker—it was more like
an electronic crackle that would happen on
and off while I was playing and sometimes
continue for a couple of seconds after
the music had stopped. I store and play
my amps in my basement. It’s a clean and
well-kept practice space, but it has been
an exceptionally humid summer, and I’m
wondering if that got to anything inside?
Thanks.
Mark
Hi Mark,
Thanks for reading and enjoying both the
magazine and the column. Regarding the
intermittent crackling in your Bassman reissue,
this could be caused by any number of
things. Since I can’t personally put your amp
on the bench and diagnose the exact cause
of the problem, I’ll give you a few suggestions
as to what it might be.
The first and easiest cause to diagnose
would be the tubes. While the amp is in its
operating mode, with the volume set at a
normal playing level, take a pencil and lightly
tap on the preamp tubes, starting from the
one closest to the input jacks. If you hear
one that seems to be making a noise similar
to the crackling noise you are experiencing,
this may be the culprit. If you happen to
experience approximately the same degree
of noise while tapping on all of the preamp
tubes, there’s only a slim chance that all the
tubes are bad, so you will need to determine
which tube may be the cause. This can be
done by “damping” the other tubes. One by
one, tap on a preamp tube while attempting
to hold or apply pressure to the glass
bottle of the remaining tubes with your
fingers. Don’t worry, the preamp tubes don’t
normally get very hot, but you may feel like
you need three hands for this exercise, so if
you have a friend nearby, appoint them the
Official Tube Tapper. If you find a preamp
tube you believe to be bad, simply replace it
and you’re done.
If the crackling does not appear to be coming
from the preamp section, perform the same
style test on the output tubes, sans the “damping”
of the opposite tube (since you may need
the skin on your fingertips to play guitar). If you
feel that this is where the noise is emanating
from, I suggest you perform one more test prior
to having a new pair of output tubes installed
and biased. Take a dry cloth, towel, or anything
that will momentarily protect your fingers from
the heat and, with the amp in operating mode,
gently move each tube back and forth in the
socket. If this creates the crackling noise you’ve
been hearing, then the cause may not be the
tube itself, but the tube socket. Occasionally,
the contacts in the tube socket can lose tension
or become dirty or oxidized, causing a poor
connection. Most times in an amp as relatively
new as yours, they can be cleaned and re-tensioned
and the problem is solved. There
are occasional instances where the tube itself is
actually the culprit, but generally it’s the socket.
As with any tube amp repair, if you are
unfamiliar with working around high voltages,
this cleaning and re-tensioning should be
performed by an experienced amp tech.
If the tubes do not seem to be the source
of the crackling, dirty or oxidized electrical
components—such as the pots, jacks or sockets—
may be compromising your Bassman’s
performance. Generally these can be cleaned
and that’s all it takes to get the amp performing
as new. Tube sockets should be cleaned
using an electrical cleaner that does not have
any type of lubricant. Remove the tube, spray
some contact cleaner into the tube socket
and then immediately cycle the tube in and
out of the socket multiple times (I’ll do this as
many as 10 times). Then leave the tubes out
of the sockets long enough that the cleaner
fully evaporates before reinstalling them.
Pots and jacks should be cleaned with contact
cleaner that contains lubricant. Spray
some contact cleaner into the opening of
a pot where the terminals attach. Rotate
the control multiple times (10 or so), then
move on to the next. If you have the ability
to access the jack contacts directly, insert
a plug into the jack, spray some contact
cleaner into the jack and cycle the plug
in and out, again maybe 10 times. (If you
can’t directly access the jack contacts, spray
the cleaner directly into the opening.) Do
this for each jack, especially all input and
effects loop jacks (not applicable on a stock
Bassman reissue). If you have multiple plugs
available, leave them inserted in all the
jacks after cleaning. This will assure that the
switching contacts in the jacks dry properly.
Once you’ve done all this, there’s a good
chance your amp will be performing up to
snuff. If you’re still having problems, then
the cause is much more deeply rooted and
you’ll need to drop the amp off at your local
purveyor of tube-amp wizardry.
I hope this has you once again happily
bangin’ on the Bassman!
Jeff Bober
Jeff Bober, one of the godfathers of the low-wattage amp
revolution, co-founded and was the principal designer
for Budda Amplification. Jeff has just launched EAST
Amplification. He can be reached at
pgampman@gmail.com.