Thanks
Some vintage amps don't even have a clunk switch, and you're supposed to just turn it on at the power point,
and this "was" one of those.

Also, Just about every serious problem will make the transformer heat up, which could be detected for auto switch off,
but that might be too late for something, so it would be better to directly monitor some voltages,
if that doesn't present clock noise to it once shielded.