music man rp65 problems

[fedcarmo]

hello from Costa Rica...i have this MM RP 65 with serious problems i guess...first since i bought it few years ago everything was kind of ok...the amp sound more or less good but when i get the gain knob up around 8 the amp increase de volumen seriously hard...like really loud and the sound was not good...seems like the gain knob before 8 does not do much in increasing the gain...poor gain from 1 to 7 or 8. Then the amp loose its "fender" tone and starting to go muddy...kind of horrible sound to my taste (at the beginning sounds ok). I found the service bulletin PDF from MM and i was checking the Bias and its said that i have to get 25MV DC on the 3.9ohm resistors...and i having problems here...i am getting one tube going red after few seconds switching from STAND BY to HI and my multimeter is reading 1640 mv ...i am not a technician...don't laugh at me ...and the amp makes a horrible hum. The only one tube amp tech in Costa Rica refused to check my amp because its a hybrid type and he only works on all tube amps.

other thing...some caps (at the can outside) were changed to 250uf...originals are 100uf...any problem?

I am posting a link with some pictures...maybe somebody can help me on this amp before i get electrocuted and more frustrated!!!

https://www.dropbox.com/sh/xdyddw96k...-H6HmhhQa?dl=0

[Enzo]

exchange places with the power tubes. Now does teh same tube red plate in its new socket? Or does the other tube now red plate in this socket? Or put another way, does that excessive 1640mv move with the tube to the other side?

My first suspect is a bad power tube. But also one of the drive transistors could be shorted.

[fedcarmo]

hello Enzo...i exchange the tubes and both tubes got red plates at the same socket...i use other set of tubes and same occur...its in the same socket where the tubes get red plates

[Enzo]

OK, so the socket circuitry has the issue. The most likely part there would be the drive transistor. How does it test out?