My new old amp hums

[Pbassred]

I just Ebayed a pair of powered wedge monitor speakers. One is fine. The other has a mains frequency hum. Symptoms;

Turning up the gain has no effect but turning up the master volume to max causes the hum to increase slightly.

I swapped the EQ sections between units and the hum stays with the amp.

There is an audible (mechanical )transformer hum. I fact, I think I can feel it vibrate.

Can transformers go bad like this? I've only ever seen complete failure.

[unclejed613]

transformers can develop "magnetic slap" over time as some of the laminations work themselves loose of the lacquer holding them together. this is easily cured in most cases with a syringe full of a wood finishing lacquer (if the loose plates are visible and easily reached) or re-dipping the transformer in lacquer. as far as the amplified hum, is it really loud or background hum? loud hum could be caused by a shorted output device (which would also cause the transformer to vibrate). background hum could be caused by a number of things, bad caps in the power supply, a loose ground wire in the eq stage, etc...