My amp won't start

[SS454]

I have this weird problem. My amp (an old 1988 Crate G60 ) gets stuck on the acoustic channel all the time. Sometimes it switches automatically, and won't change back until I whack it on the head real hard. This seems to do the trick most of the time. Does anyone know what the problem could be?
And don't say get a new amp, cause there's something unique about this particular one. I've tried other G60s and they all sound like shit. In fact, this is the only amp I've heard that I like, short of a Mesa or a Laney full stack.

 

[James Argo]

It's an old one anyway, right ? But if you still like it, what can I say than bring it to repairman. Something like old switches could have it's time to be fixed. Or bring it to your local music store, and find the technician guy to take a look what's going on. You'll see no help in this thread to guess sumethin' we should take a look.