Try lifting the A/C ground wire out of the circuit. (use a 'cheater' plug)
Try grounding the chassis of the amp to the A/C ground with a bit of wire..
Try it from a different A/C outlet
My (bad) guess it probably is a dying capacitor. Some small signal level one(s)
Try grounding the chassis of the amp to the A/C ground with a bit of wire..
Try it from a different A/C outlet
My (bad) guess it probably is a dying capacitor. Some small signal level one(s)