[Reece]

Is yours the table model shown on Radio Museum with the built in speaker? With 201A tubes, 6 volts for filaments would be correct, cut down to 5 volts by the filament rheostat. B voltages on sets like this would be usually 22-1/2 for the detector, 45 for other tubes, and 90 for the output tube. That's what I'd start with. Check the horn driver with an ohmmeter first: could be open, in which case you'd sub an ordinary output transformer primary there connected to a modern PM speaker. Could use any transformer in the junk box from an AA5. Put your voltmeter across the filament terminals of a tube, start with the rheostat off and don't go over 5 volts. 201A's could have a max of 135 on the output tube but would work better with C voltage of about 4.5V to bias the output tube. Does your set indicate connections for a C battery?