 The earliest so-called "farm radios" used the "A", "B", and "C" batteries typical of 1920s radio sets; these farm radios were identical to those used in cities.Somewhat later, farm radios were made to be run on 6 volts from a car or tractor battery, using an electromechanical vibrator to create a pulsating DC current that could be stepped up though a transformer to create the high voltage needed for the plates of the tubes- exactly as contemporary car radios did.Other farm radios were designed to run on 32 volts DC, from a bank of lead-acid storage batteries charged from a gas powered generator or a wind-charger.