mesa mark III red plating

[pstanleystrat]

Hey guys ! I have a 1987 Mesa Mark III that is red plating on two of the power tube sockets, one El34 and one of the 6L6, this is a simul-class model . there are a few caps that have been leaking some so wondering if a re-cap is in order.... and of course new tubes !

Paul

[pdf64]

Are the caps leaking goop or dc?
With the power tubes removed, how do the Vdc at the red platey socket terminals compare to the others?
Is the amp stock or has the bias been tinkered with?
Were the tubes selected for use in Mesas?

[Leo_Gnardo]

With the power tubes removed, how do the Vdc at the red platey socket terminals compare to the others?

What pdf64 said. ^^^

Especially pin 5, the control grid.

First suspect is you have an output tube that is failing, causing its grid voltage to drift positive, and that would cause its parallel tube grid to move in the same direction.

Second suspect, the capacitor bringing signal to pins 5 is leaking and must be replaced. Although Mesa used "super reliable" orange drops in most of their amps, in recent years I've found some of them failed, leaking DC.