Designed for 115vac input...

[petemoore]

The FC Speaker amp is nice, but the 6v6's are redplating.
Immediate reason for this is the design was during the 115vac design period in which it was intended to run.
This period had no notion that 120vac or 125vac would become the norm.
10w Zeners ?
Or is there another elegant way to bend the design to operate correctly using 120vac primary supply ?

[tboy]

Immediate reason for this is the design was during the 115vac design period in which it was intended to run.

That wouldn't be my first suspect as a cause for red plates. Have you eliminated other possible causes?

[trevorus]

That wouldn't be my first suspect as a cause for red plates. Have you eliminated other possible causes?

Definitely check the bias and such. Usually tubes can handle a bit of over voltage. Red plating usually means there is too much current being pulled through the tubes. Over-volting usually results in inner arcing of the tubes, if I'm not mistaken.

[Enzo]

I'd also have to think a 5-6% increase in mains voltage - and consequently all the inner voltages - wouldn;t by itself cause red plating. These amps shouldn;t be designed THAT close to the edge.

WHat is the bias situation? What DC voltages are on the grids?

[petemoore]

understand

I was told and read responses to similar redplating threads which suggested a voltage drop at the input instead of re-working bias
...@@Rate that's why I approached this thread with the 115vac angle.
In light of the responses though, I'm changing the initial approach to include the typical going over and bias check/rebias.
Thanks for helping me decide on my approach !