Amp Troubleshooting and Repairs for Road Dogs

02.25.2013 Gibson GA amp

One thing you can count on if you’re a touring musician is that at some point your amp is going to stop working or fail to operate correctly. That’s why it’s always a good idea to travel with a backup and to have some simple amp fixes, which are all many failures require, within your skill set.

First, a word of caution. There are dangers associated with major amp repairs, since transformers can retain their raw voltage and deliver serious, harmful shocks unless they are properly discharged. But tube trouble shooting, re-soldering, pot cleaning and wire repair can often solve a problem enough to get one through a gig or tour without risking electrocution or shelling out bit money to a repairman on the road. Those without training in dealing with charge-bearing electrical devices would be wise to leave the transformer alone — and nobody should work on an amp while it’s plugged in, ever.

Here’s an example of a quick fix I had to make last year in Kent, Ohio. A sloppy soundman decided it would be fine to roughly tilt one of the small combo amps I was playing through against the wall to angle the speaker up toward the boom stand he was using to mike the amp. The L-shaped jack connecting the speaker wires to the combo’s amp section struck the corner of a low shelf at a vulnerable spot, splitting the wire and input at the elbow and killing the signal. Grabbing a wire cutter, I snipped through the dangling split, stripped the wire and exposed the two metal posts behind the jack that the cable would normally be soldered to. With no soldering iron in the bag, I popped a piece of chewing gum into my mouth while I twirled the wire around the posts, then used the gum to hold it in place and wrapped electrical tape around the area to hold it all together. The next day I replaced the cable at a Dayton music store for a couple bucks before the next gig. Tools used: electrical tape and a chunk of Bazooka Joe.

Of course, things are rarely that easy, but as a general rule always carry a can of tuner spray (available at any Radio Shack), pointy noised pliers, flat- and Phillips-head screwdrivers, electrical and duct tape and — if you can — a set of replacement tubes in a protected, cushioned container.

The latter will get you out of many tangles. Tubes inside of amps crack in transit, even when it seems like there’s no logical reason why, and burn out exactly when they shouldn’t. And even less obvious problems — like a suddenly distorted tone or a drop in output volume — can be related to tubes. Let’s take the latter as an example. If your normally screamingly loud amp — a handy thing to possess in rock clubs with inadequate PA systems — has adopted a more conversational volume, consider replacing the power tubes. Capacitors, resistors and transformers can cause this kind of trouble, too, but it’s often the power tubes. If replacing the tubes doesn’t work, swap the new power tubes back out with the old ones and try the preamp tube. There’s a better than 50-percent chance a tube is the culprit. Another tip is to consider replacing capacitors and resistors every decade or so, since they do have a limited shelf life. That’s preventative medicine.

Other problems can be traced to tubes as well. A rumbling, thumping sound — almost like wind crossing a microphone — can often be caused by a bad or loose output tube. Conversely, squeaky high-pitched sounds or crackling noises may be the fault of a bad or loose pre-amp tube. Again, switching them out with replacements will reveal if they are the culprits.

If swapping out tubes doesn’t work in these situations, it could be a job for that can of spray-on tuner cleaner. Amp sockets become dirty and rusty, and a quick squirt and some patience while they dry can sometimes get the fix done.

Of course, all this tube juggling takes time that you might not have — especially if the problem surfaced during soundcheck or, even worse, line-check. This is why it’s good to carry a second amp. That back-up doesn’t have to be a doppelganger of your Marshall Plexi or whatever you blast through. You just need to get through a gig in an emergency, so a small inexpensive transistor amp will do, or a box like a SansAmp. You can take a deeper look at the problem, or find a repairman, when the show is over. 

If you’ve got the budget, carry at least one replacement speaker, too. An amp with efficient tubes that still delivers fuzzy tone may be suffering from a speaker problem, like a tear in the cone or a separation from the cone and mount. To deduce this, have somebody else play guitar through the offending amp and touch each speaker. If one is moving in manner that feels less anchored and “soft,” that’s likely the culprit. Speakers in a multi-speaker cabinet can be unplugged and run as single speakers for a short period of time, which will also reveal deficiencies. And remember, these days there’s no legit reason for soldering speaker wires to speakers. Leave horseshoe clips unencumbered by solder so they can be slipped on and off when repairs like this need to be made.

Another thing to carry is several replacements for all the fuses in your amp. A blown fuse can shut you down and it takes just seconds to pop another in place. This is an easy fix most of the time, because it comes with a clue: the “on” indicator lights in amps won’t go on if an amp’s fuse is blown.

As long as you’ve got a spare amp of some kind available, it’s best to leave more complicated fixes to the pros. Over-reaching one’s amp fixing skill level is a great way to inflate your repair tech’s bill!