I was worried more about current than voltage, so I connected power
valve filaments in series and drive them with a current source.

Yes, that's exactly what I do.


I spent some time wondering about high unregulated current passing
through the same conduit as the carefully-filtered HT and bias
supplies. Regulating all the filament supplies relieved the worry, but
I don't know if it was actually worthwhile.

All the suplies will be DC, as you say. No choice with DHTs.

I think I'm going for twin supplies rather than one connector. Most of
the filaments are very low voltage low current - something like 4 volts
at 120mA max. The output valves if 2a3 would be 2.5v at 2.5A. Would
need four connections for those.