Lee, you have a 'scope, you might have to use a cord cheater to unground it. You can center the Time/Div to show 60Hz (10 msec/div works good for me) and run the probe around inside the chassis of the amplifier to locate the hotspots (hum). I was surprised where I found the most hum, and it was easy to fix by moving the wire. If there is a loose AC connection, your 'scope will read off the scale.
Mark