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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 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, 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 firstname.lastname@example.org.