A magnetron constructed by locating a pair of permanent magnets in a vacuum container which is an anode cylinder (i.e. shell) of magnetic material and has upper and lower covers of magnetic material to form a magnetic circuit. A high frequency resonator is formed by attaching anode vanes directly to the internal wall of the anode cylinder and providing a film of highly conductive material on the internal wall of the anode cylinder between the anode vanes. Terminals for the supply of power to a cathode disposed between the permanent magnets pass through a hole in at least one of the permanent magnets and one of the covers of the magnetic material. An antenna, or probe, extends out of a hole in the side wall of the anode cylinder, and heat radiative fins are attached directly to the external wall of the anode cylinder.