My old Atwater-Kent used two batteries, A and B
"A" voltage was for filament and it came from the A-battery; "B" voltage fed the plates and (oddly) came from the B-battery. (B+)
Sometimes a "C" cell was used to power grids, but usually a rheostat could provide it, tapped off of the B+ line.
Then the power company came along an put up all those dag-burned poles and it all changed.
Lot of good men lost putting up those wires, back in the day, yessiree.
No one even remembers the sacrifices made to bring utilities to these here parts atall.
Be careful with 120 vdc field wiring, it can burn and/or kill.
In fact, high DC voltages are even more dangerous than wall outlets.