He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

James. )