Abstract: A magnetron provided with a filter circuit for suppressing leaking of the electromagnetic wave of the magnetron. First and second choke coils have their respective first ends serially connected to two externally protruding leads for supporting a cathode filament of the magnetron. A feed-through capacitor is parallelly connected to the second ends of the first and second choke coils respectively. The feed-through capacitor is constituted by a dielectric ceramic material having a relative dielectric constant .epsilon..sub.s which satisfies .sqroot..epsilon..sub.s .ltoreq.50, whereby sound pressure produced by of the feed-through capacitor is reduced without increasing the size of the feed-through capacitor and while keeping the necessary breakdown voltage characteristic and necessary electrostatic capacity.

Abstract: There is disclosed a magnetron whose oscillation frequency can be easily adjusted. The magnetron comprises a cylindrical anode, several anode vanes radially arranged around the axis of the anode, and two strap rings of the same structure. Alternate ones of the anode vanes are connected together by one of the strap rings. The remaining anode rings are connected together by the other strap ring. The two strap rings are displaced circumferentially relative to each other by a given angle centering around the axis of the anode.

Abstract: A dark heater is produced by a method which comprises coating the first coating layer made of an insulating material with a suspension containing heat-resistant particles having a high thermal emissivity, such as W particles, while 0.5 to 1.5 wt. % of a volatile matter such as water remains in the first coating layer to form a dark coating layer. Since the suspension having a low viscosity can be used, the thickness of the dark coating layer can be made highly uniform and the emission characteristics of the heater can be stabilized.

Abstract: A switching power supply, in which a series circuit consisting of a primary winding of a transformer and a controllable switch is connected with a DC power source and a secondary winding of the transformer is connected with a first voltage source outputting the voltage developed across the secondary winding during the on-period of the controllable switch and a second voltage source storing the exciting energy of the transformer during the off-period of the controllable switch by using the exciting inductance of the transformer as a current source, a series circuit consisting of the first and the second voltage sources being connected with a load. Owing to this construction, even if voltage-current characteristic of a load having constant voltage characteristic, such as a magnetron, vary due to variations in the temperature, etc., the output voltage is automatically compensated and a stable electric power can be supplied to the load.