: A power supply apparatus for use with a high-frequency heater employs a transformer for increasing the voltage of power provided by a commercial power supply that has been converted into a high-frequency by a transducer. The transformer feeds the converted power into a load that has unidirectional electrical current characteristics, e.g. those of a magnetron. The generated voltage is reduced by a tuning circuit connected to the transformer and having a resonant frequency higher (preferably a higher harmonic) than the operating frequency of the transformer. The result is avoidance of corona and arc discharges and an ability to reduce the insulation withstand voltage between the windings of the transformer.
