Today’s tip comes from one of our resident guitar gurus.
Try running your old tube guitar amp on a variac. A variac allows you to lower the supply voltage to your amp, which can radically change the sound of older amps, often for the better. Guitarists report warmer, more saturated distortion on older amps when supplied with slightly less voltage. The procedure is simple though potentially dangerous to your amp so use extreme caution (if you aren’t sure what you are doing, stop; you can really damage your amp doing this). Connect the power cord for your amp to the output of a variac. Set the variac for normal output and power up your amp. Let it warm up at normal voltage for 20 to 30 minutes. Then begin playing your amp at a moderate volume while SLOWLY turning down the output voltage of the variac. It’s best to have a voltmeter connected to this output as well so you can monitor the voltage your amp is getting. By the time you get down to around 100 volts you should notice the sound of your amp changing, particularly if you are driving it somewhat hard. It’s a good idea not to go below about 90 volts, but you may find that the sweet spot for sound is between 90 and 100 volts, depending upon how hard you are driving the amp and what sort of tone you like.
Again, we stress, be careful with this. You can damage your amp or radically shorten the life of your tubes. If you find the sound to your liking it may be worth the potential risks to your gear. If not, we suggest you run with normal voltage.