1968 JMP100 12-series...NOS?

[kek]

Since I'm only switching from 490 to 460V - i.e. roughly a 6% change, I figured I'd leave the bias alone and live with the compromise. Set it for maybe 72% in high voltage mode and 66% in low voltage mode. Then I'd use the third pole to switch in the extra 50uF on the PI in high voltage mode.

BUT: is it safe to switch both HV AC and B+ on different poles of the same switch?

What is the exact type and model of switch you are using?

Why would you need to have the anode voltage over the switch element in order to add more capacitance to the phase splitter rail decoupling? Wouldn't it be better to wire it with 0V over the switch?

Maybe you can draw a schematic showing what you want to do.

[Marshall SL12301]

WOW! That is amazing. very inspiring for a guy like me that is about to try to build one

[Roe]

looks great, although I'd consider pulling the green wires on v1 and v3b further away from the blue wires to prevent potential oscillation

[shakti]

I've poked around on them without it seemingly affecting anything. On V1, threading them through the Board like that was probably something I'd seen on an old amp, and I could possibly cut some wire length by not doing that. But V1 does not seem to be the culprit anyway.

On V3, I don't necessarily see how I could easily get the grid wires much further away from the plate wires. But since the problem With this amp appears to come from the PI or the OT, then it's worth another shot. At least if I decide to rebuild it....