Peavey Ultra-120 Head red plating one tube

[gcb34]

I have a red plating Power Tube 6L6gc after it warms up. Anyone have a suggestion or schematics? Looking at the back of the head it is the back row tube on the input side. The plate voltages on all four tubes looks ok. the two front tubes have 36ma. the back two are .02ma. That's as far as I got.

[captntasty]

Switch the red plating tube with one that isn't... does the red plating occur in the same socket or does it stay with the tube? This will tell you whether it is the tube itself or the socket (and components in all it's associated circuitry) is bad.

[gcb34]

Sorry forgot to mention that in OP. I did swap tubes and it stayed at the socket.

[Gtr_tech]

Clean and retension the contacts in that socket as a starting point. If that doesn't take care of it there's prob'ly cracked solder on the board they are attached to

[gcb34]

Will do... Thanks! I'll let you know how it goes.

[gcb34]

Did not help. When I use the low input no red plating. It's when I use the high input. I attached the schematic.

[Gtr_tech]

Sounds like oscillation then.....