Low voltage
A similar device is the vibrator power supply, used to power electronic valve radios from low-voltage batteries. Low voltage DC from the battery is chopped by a trembler circuit and this pulsed square wave used to drive a transformer, providing the 90V or so required by valves. As this application is more frequency sensitive, the vibrators were generally a separate unit, with a more stable frequency tuned reed, apart from the transformer. This transformer had output tappings for the 90V HT and also the 22V grid and 6V heater circuits required by valves. In many cases, the transformer was the same unit used for powering the radio set from domestic mains, using the same secondaries but with an additional primary winding at mains voltage.