Abstract: PCT No. PCT/JP78/00033 Sec. 371 Date July 30, 1979 Sec. 102(e) Date July 23, 1979 PCT Filed July 27, 1979 PCT Pub. No. WO79/00329 PCT Pub. Date June 14, 1979A magnetron is constructed with an annular wall anode structure including a cylindrical wall first section of smaller diameter or cross-sectional area, and an annular wall second section of greater cross-sectional area. The first and second sections are integrally formed as part of the magnetic circuit and are interconnected by a drawn or flared wall third section in a preferred embodiment. The input and output elements are coupled to the larger second section for enhanced spacing and cooling. The anode and cathode assemblies are mounted primarily in the first section. Internal and external permanent magnet assemblies and enclosures are described with an internal magnetic pole piece for improved lay-out of lead wires and to permit use of solid rod section permanent magnets.