A magnetron having eight anode vanes (2) arranged radially inside an anode cylinder (3) and a helically coiled, directly heated filament positioned along the anode cylinder. The magnetron oscillates at a basic frequency of 2450 MHz. The external diameter of the helically coiled, directly heated filament is in the range of 2.6 to 3.2 mm, and the diameter between the internal ends of the anode vanes is in the range of 7.0 to 8.0 mm.
