1. ABANDONMENT IS NO WAY TO TREAT AN AMP
Got a tube amp that’s starting to sound a little tired and ragged? Maybe it’s lacking in sparkle and harmonic content, noisy, and/or loose in the low end?
If it were a guitar, you would probably change strings, maybe check the intonation, or treat it to a professional setup. The recourse of too many amp owners, however, is simply to sell the thing and start fresh with a new one.
Instead, try giving old faithful a second chance via these few simple checkpoints, as periodic maintenance can breathe new life into a hard-working tone machine. (Note: Tube amplifiers contain potentially lethal voltages, and any internal work—such as voltage checks, soldering, and even internal cleaning—can pose safety concerns and should be done by a professional.)
2. TUBES CAN SOUND TIRED LONG BEFORE THEY FAIL
Many of the above-described sonic symptoms can be attributed to tired tubes alone, so unless you (or your tech) can pinpoint a specific need elsewhere, a fresh set of tubes is usually a good idea—especially if you know they haven’t been changed in a while.
How often you need to change them depends on hours of use and how hard you run them. Output tubes need to be changed more frequently than preamp tubes, and should be rebiased when installed in many amps (check your manual). To check for tired preamp tubes, acquire a good new one and sub it into various positions to see what perks up your front end, then replace that position.
3. FILTER CAPS ALSO NEED PERIODIC REPLACEMENT
Just because those big electrolytic capacitors—known as “filter caps”—are soldered in place doesn’t mean they are permanent. Any amp that’s more than 15 or 20 years old and is still running on its original filter caps is probably a candidate for new ones.
They might still work fine, but they also might be depleting your low end and overall tonal solidity—and might be ready to fail at any moment. The big ones are the most obvious candidates for replacement, but the smaller caps in the preamp section of the board also occasionally need attention.
4. TUBE SOCKETS MUST BE TIGHT
Older amps, and especially those that have lived through several tube replacements, can usually benefit from having their tube sockets’ receptacles tightened. This is a job for a professional repairman because there are high voltages present, but it’s easily done with a little careful pressure from the tip of a jeweler’s screwdriver.
During such maintenance it’s usually a good idea to check for any corrosion at the pins and halt it with a little squirt of contact cleaner. Short of tightening the pin sockets you can do this one yourself: Spray some cleaner on the pins of an old tube and insert it in and out of the socket a few times to distribute the cleaner.
5. SCRATCHY POTS SHOULD BE KEPT CLEANED
Sometimes a few quick twists will clean up a scratchy volume or tone control for a while, but it’s best to squirt contact cleaner into the access holes in all potentiometers from inside the chassis and rotate them swiftly to clean up their tracks.
If this doesn’t work, you know it’s time to replace the pot entirely, which is usually not a costly item. While your tech is inside the chassis, it’s also a good idea to use a can of compressed air to blow out the dust, insect carcasses, and cobwebs, and to check for any dodgy looking wires or cruddy solder connections.