I recently aquired an RP 112 65.
However after playing it for a few hours it started to hum. Now I new it most likely needed a cap job, so no surprise.
I have replaced all electrolytics in the amp. Some values seems non existant though so I took what I could get.
Some differences in values now.
The 150uF caps next to the diodes are now 100uF (would it be better to go up in value?)
The 400uF next to them are now 470uF
and all the 20uF caps are now 22uF.
I measured the old caps and they had drifted enormously! The 400uF caps were at 512uF!
I started the amp up and it hummed loud and red plated on the first of the two 6L6 GCs.
Turned it of, switched positions on the tubes. Same thing. Red plating on the first one.
So no bad tube.
Looking at the pcb there are a burn mark under the two large zeners so I replaced those.
I'm trying to take measurements on pin 5 and get very different results on the two tubes. Also when I measure across the bias resistors.
I have tried to alter the bias with the bias pot and got rid of the red plating but the amp now humms in what sounds almost like tremolo oscillations.. Like a wobbling humming.
I'm not that knowlegeable on MM amps and believe that the tubes are somehow driven by the transistors below the bias pot?
I am lost right now however and need help with suggestions..
Only thing I can think of now is that the new cap vaules made it go bananas.. But the burn mark tells me that the old caps perhaps has been drifting for a while..
It is the RP 2165 with GP-3 board.