Hi Wayne,
I assume you are trying to run a BC-348 with its original dynamotor. For power, you can run the filaments at AC from one source and the dyno on DC from another. The DC supply would only require about 2 amps. It wouldn't take much to cobble up 24 VDC at 2 amps with a decent end electrolytic to assist the starting surge. Unfortunately I have never had that opportunity with a BC-348 since my 348's and 224 were all converted before I got them. However, I did run several Command receivers using one of those Knight or Eico battery eliminators that were used as car radio substitute power sources back in the day. Those go for relatively cheap at hamfests. At low current with silicon rectifiers, the voltage can get a lot higher than 12 VDC.
One of the 3 Command receiver dymos I tested was a Continental Electric that was size and plug compatible but had original gray paint. Here are my notes from an article written several years ago.
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"While the same size as the other two, it was capable of up to 85 mA at 250 volts and may have been intended for a later VHF Command set, many of which also came with gray paint. I not only lubed it, but had to take it apart to repair the flaking rubber-covered wires to the base plate connector. Afterwards I tested it. It ran beautifully at 24 volts input and 250 volts at 60 mA output to my two-series connected (7 watt) night lights. I could not test it at 28 volts input, because my Knight battery eliminator power supply topped out at 24.6 volts given the greater current draw at 1.7 amps instead of 1.1 of this more powerful dyno. At just 5 volts input, the dyno was still pumping out 41 volts at 20 mA.
To no surprise, the 3 dynamotors easily powered the Command receivers."
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You can run filaments on about anything, but if you use half wave DC (direct diode off AC with no filter caps) the filaments will see an equivalent heating DC power of 0.707 times the input AC.
Best wishes experimenting es 73,
Rich KB8TAD