I can remember having at least one amp where the power switch had 2 “On” positions, and that was supposed to help prevent shocks. I was told that it flipped the ground from negative to positive. Is that correct? This feature seems to have disappeared. Was it found to be unsafe?
On tube amps I’ve seen two switches, but usually one was to turn on the thing and the other was to switch from standby to ready. I believe it’s because it takes time to warm up the tubes before you can hear anything, so instead of turning off all power to the amp and thus causing a delay when you turn it back on, you can just hit the standby switch, thus causing the tubes to stay powered but nothing to come out the speaker.
when plugs became polarized this feature would no longer be needed. if it was as you said then that switch would have switched which wire from the plug went to the chassis.
I’m confused – is this the same as the set-up you see on tube amps (standby + on) switches, just in a different configuration? The ones I’ve seen have had three-prong plugs, plus the usual two switches.
I’ve always thought standby just helped keep the tubes warmed up, and maybe protected them a little bit. How? I don’t know. Maybe if you didn’t want any hum or noise. I don’t think it prevents some jerk from smashing into it to hear the spring in the reverb make a loud annoying cartoon sound, but I’ve never experimented with that (because I hate finding replacement tubes)
Unisolated amplifier circuits were found to be unsafe, and I doubt that anyone makes them anymore.