PURPOSE:To ensure sufficient power for heater preheating by rectifying a high- frequency output from a winding for heater-preheating power supply by a rectifier circuit on the preheating of an electronic tube, smoothing the output and accumulating it in an accumulating circuit. CONSTITUTION:The state of light load is brought on the preheating of a heater 2, and sufficient voltage is generated for the preheating of the heater 2 after a capacitor CH for the smoothing and charging of a charging circuit 4 is charged sufficiently even when charging currents rectified by a rectifier circuit 3 from a winding SH for heater-preheating power supply and fed to the capacitor CH are slight. Consequently, the preheating operation of the heater 2 is conducted enough by power charged and accumulated to the capacitor CH. When the preheating of the heater 2 is performed, the conduction of anode currents to an anode 1 is enabled, and currents fed from a winding SA for supplying anode currents flow.
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