super high plate voltage

[pdf64]

A good indicator for whether the PT is being supplied with its intended mains voltage is the heater voltage - what's the heater voltage, eg 6.3 Vac?

[dmartn149]

Thanks pdf64, (and everyone else who offered advice on this) I just now put the power tubes back in (I had removed them after G1 suggested oscillation) and rechecked plate voltage with the analog meter set up properly. It's at 650v which is just barely within max design value for this tube. Heater voltage is 6.7 so I guess it's good to go.
Thanks again everyone!

[g1]

If you still want reduction, you could put a bucker transformer in the primary of the PT to bring the heater down to 6.3 and also reduce the B+.
It could be either internal, or external, like R.G. Keen explains here:
Vintage Voltage Adapter

[dmartn149]

Thanks g1 I'll probably just use it as is.

[pdf64]

...It's at 650v which is just barely within max design value for this tube...

Voltage doubler supplies are often rather saggy, so the 650V HT at idle may be <600V at high signal levels, hence tube stress is less than may be apparent.