- Is there any reason to avoid DC?

- What would be an appropriate DC voltage?
Is a standard 12V reg OK or should I shoot for 12.6V or what else

I have done that in other receivers.

Regulated dc is fine for the filaments. In theory, dc may cause the
filament to wear out quicker than ac, but we are picking at straws. With
dc, the electrons leave one side of the filament, while ac balances out the
electron flow. I have never had a dc filament from such a regulator
conversion fail, though.

12 volts is find for 2x6 volt filaments in series.

I first applied this to a Hallicrafters SX-101. That had a separate
transformer for the filament and was easy. My shack was cold and I had a
120 volt heater in the shack. When it came on and off, the voltage on the
filament of the oscillator changed and there was a slow drift (especially on
10 meters). Although the plate voltage was regulated, I soon realized it
was the change in filament temperature that caused the drift. A secondary
benefit was realized from the conversion because the hum modulation of the
cathode of the 12BY7 was removed and cw signals sounded cleaner.

Colin K7FM