Thanks, Pete, and I had looked at that. The manual only shows it being
connected to the companion transmitter (HX-20) for power, but does not
show what voltages will be comming out of the transmitter power socket.

I'll hope there is someone with this on the operating table that can
supply (hoho) with the voltage requirements.

Well looking at the HR-20 Manual on bama, page seven shows the supply
volyages as either 6 or 12 volts for
the filiments and 275 to 350 vdc for the plate supply. The schematic
on page 15 shows the interconnect.
And who ever supplied the manual even has the jumpers marked for
operation.

Thanks for the correction. Don't know how I missed that!