I'm servicing a low end Melody guitar amp. Guitar amps are something I do not normally service. It looks like it's from the 1960's. It has a speaker, three inputs, but only one volume control. There's a plug for a foot pedal and controls for volume, tone, speed and depth. Internally, there are five tubes and NO ac input transformer. It looks as if someone has replaced a few parts. I can't tell whether or not the circuit has been modified. The customer complaint is that it hums when idling. There is a small amount of background hum. I wouldn't exactly call it objectionable. The audio output is not too bad. In doing a basic leakage test with my Sencore PR57, the leakage current reads 550µA on one side. The other side is worse. The meter is pegged even before I push the leakage current button on the probe. When I press the leakage button on the probe, the speaker emits a loud hum and the meter pegs all the way.
Are these sorts of readings to be expected on an amp like this?
Thanks for your reply.