Power amp humming - help please

could be a number of things (ground loop, bad caps or power supply, etc. etc.). however, i've often found the culprit to be a slightly loose transformer, which can be fixed simply by screwing it down tighter. make sure you disconnect the power from the amp for a couple of days before you screw around with it

Thanks a lot Johnson - I will have to try that - I will be careful as you warned me.

OK--typically it's a hexagonal nut in the middle of the top of the transformer,

Thanks again Johnson...