"Clipping" sound from 210 Sixty Five

Hello everyone:
I just got a MusicMan amp, a 210 Sixty Five. It is a potentially nice amp, everything seems to work except...
instead of the nice tone it should have...
1) it has a lousy "clipping/distorted" tone at all volumes and settings, and
2) it doesn't get very loud.
As a matter of fact, if you turn it up to 10, it is only as loud as a much smaller amp on 1 1/2.
So far, I've checked the El-34 power tubes, the 12AX7 phase inverter tube, the speakers, and sprayed the pots & tube sockets with contact cleaner. All check out.
The person I bought it from does not know when or how this problem occurred.
Any ideas as to what could cause this? It is a buzzing/clipping sound, not a hummming sound. And little volume.
Thanks for any ideas!
Cheers -
Richard

Just a wag but have you checked the caps? THat amp is now 30 yrs old and the elctrolytic caps could be shot. THis will do all sorts of things ranging from just little low end response to smoking a transformer. Start there and let us know. It really sounds like a trip to the vet is called for. Mike.