Clean the amp with deoxit. Especially the switch that makes the problem when you try it. Especially clean the potentiometers deoxit will do a great job I. The deoxidizing department.
Worth fixing?
I have a Rotel 951 CD player paired with an Arcam alpha7 amp and Paradigm speakers. One speaker cuts in and out occasionally. (Which doesn’t happen with the turntable). Swapped it with an Onkyo CD player and problem solved so it’s clearly the CD player issue. But it has some sentimental value. Ideas about what the problem might be and is it fixable by me. Or should I junk it.