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Right next to the on/off switch on many tube amps is a second switch labeled “standby”. It’s that switch that silences your guitar amp without actually turning it off, which comes in handy when break time rolls around at rehearsal or at a gig.

What you might not know, however, is that while that is a conveniently useful function of the standby switch, that’s not the main reason it’s there. First and foremost, the standby switch has a much more important role—protecting your amp’s tubes.

It’s kind of hard to believe that tubes are even still around. They seem so archaic—prehistoric, even—in this high-tech modern age of digital wizardry. Electric guitar amplification is one of the very few arenas in which tube technology still thrives, and the basics of tube operation haven’t changed much. Take warming up, for example.

Just like old radios, TV sets and the room-sized ENIAC computer of 1946 (which used 17,468 vacuum tubes), tube guitar amps need a minute to warm up after you turn them on. The science is pretty complicated, but suffice to say that tubes have to be hot in order to work (something about emitting electrons). In fact, they have to be really hot—like, glowing hot—before you can put a strong amount of electricity through them, and it naturally takes a brief period for them to reach their proper operating temperatures. If you turn a tube amp on and immediately crank it to full volume before the tubes have had a chance to warm up, you risk damaging your amp.

Therein lies the real utility of the standby switch. It allows the amp to be turned on but keeps full voltage from reaching its power tubes until they’ve had sufficient time to warm up, thus protecting them and prolonging their life.

You’ll notice that the switch itself usually isn’t labeled “on/off", but rather “on/standby". When you first turn your amp on, you want the switch to be in the “standby” position, in which no sound will be produced while the tubes warm up. Then, anywhere from 15 seconds to a few minutes after powering up, flip the standby switch to the “on” position, and you’re ready to rock at whatever volume you like.

At a rehearsal or gig, in fact, a good modus operandi is to first turn on your amp in standby mode, then go about setting up the rest of your gear—adjust pedals, run cords, tune up, order a drink, wash your hands and so forth. That usually takes at least a few minutes, after which you then flip the standby switch of your properly warmed-up amp to “on”, and off you go.

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