Wingnut,
Did you try dis-connecting the input cable at the amp while it's playing ? If you still have hum, at this point--the problem is internal to the amp. If the hum is gone--re-connect the cable, play a record and lift the tone arm off the record--no hum, problem is mechanical in the turntable--still hummms, problem is in cartridge, tone arm, and / or cable. Ron Rich