Amp showing its age?

My guess would be one or all. Power switches build up carbon from arching and become resistive after decades.  Electrolytic power supply capacitors, final stage driver transistors,  new output transistors.

Clean it, get the bias adjusted, and measure the power caps. 

My amp is 50 years old, still 100% stock inside. 

@mswale  Too late, already sold and replaced. Oh, well. I was already considering an upgrade. Lucky you on a 50-year amp. What is it, Crown? Early ARC? An amp like that would be a conversation piece if you started a thread on the subject in this forum.

@hickamore it sounds like you just really wanted a new amp. I totally get that. 

It's none of them, it's a Hitachi, one of the first FET amps, sounds like tubes, it's huge, and is 60lbs. Tested the power caps several months ago, they were all good. But just measured the bias last month and the right channel is a little off 5%, left Chanel was perfect. Will adjust it next time it get pulled out of the rack for cleaning.