mesa boogie become monophonic

[eggle]

hi people, i wondered if anyone knows about a problem i have.. i have a mesa boogie f-30 amp. when i turn to channel 2 (overdrive) gain set at around 6-7 ish....when i turn the volume up to say 5 or 6 the amp squeels like a pig, with a guitar plugged in or not.if you tap the amp its like a live mic and its becomes microphonic. so i change all the valves, and problem still there. so i tap all tubes and the 2nd preamp sounds very clunky when i tap it with a chopstick.So replaced this and all valves again and still the probelm is there.So now i remove the amp from the chasis and start tapping around the caps with a chopstick and when i touch the cap that is right by tube 2 the amp becomes worse and screams more. so i change this cap. problem is still there....any ideas please? i have phoned mesa themselves and spoke to the tech and he is stumped.

[Don Moose]

I'd look in that immediate area for bad solder joints or broken traces, then at V2's individual pin sockets - one of the grids' pins (especially the one that cap connects to) may be loose.

Hope this helps!

[eggle]

thanks for that, ill have another look later, if anyjoy ll let you know...cheers jas