Question about hum from speakers


I know there's at least one amp engineer here... I'd like some help.  I bought a used solid-state amp from ebay; the ad read " McCORMACK POWER DRIVE DNA-.5 Deluxe REV B POWER AMPLIFIER - EXCELLENT CONDITION!"
Well, I swapped it in, replacing a Dynaco Stereo 120, and there's a hum from both speakers.  I have to believe that the seller was well aware of the hum.  What I'm wondering is, is the hum a result of some electronic component(s) in the amp failing (or having failed), such that it's salvageable by replacing the bad component(s)?  Or would that be hoping too much?
bhakti-rider
bhakti


That is a safety ground. Lifting the ground could lead to fires and lethal voltages at the case. That's why the ground wire in your outlet is required to be the same gauge as your power line (12 or 14 gauge) : So in the event of a short to the case a breaker will trip.


The best way to fix it is to identify the root cause. Often this means making sure multiple equipment is on the same strip or outlets or adding isolators to any external coax lines (for cable/internet or outside antennas).


Unfortunately it's no one solution. 

Best,
E
Post removed 
My ground loop was caused because I have my stereo also hooked up to the tv cable box for watching some tv shows.  Buying the following isolator completely eliminated the hum.
Jensen VRD-1FF IsoMax Digital RF Isolator

https://www.parts-express.com/jensen-iso-max-vrd-1ff-75-ohm-inline-digital-catv-isolator-hum-elimina...
Try unplugging components until you isolate the component causing the hum.  Also note, that I have had RCAs on my turntable that were not insulated enough and these caused hum, which when replaced, went away.