Thanks one and all for the responses. You've convinced me I am
over my head on this one, and that it is time to find someone with
a clue. Any recommendations in the DC-Baltimore area?

FWIW, this amp was substantially rebuilt by James Bongiorno a few
years back, so I do not think old age is the cause of the
problems. The list of other possibilities nonetheless exceeds my
ken, so it is time for me to seek a professional.

Phil Anderson