Abstract: A cathode assembly for a magnetron having a lower end shield for supporting a filament joined thereto and an insulator supporting a lower end shield on which the filament is mounted, the insulator being bonded to the lower surface of a flange on the lower end shield utilizing a ring shaped metalizing portion at the upper surface of the insulator which also joins a side lead to the lower end shield, and the insulator being fixedly mounted in a lower magnetic pole to exactly center the assembly about the central axis of an anode cylinder, thereby minimizing the quantity of dark current generated by escaping thermions, resulting in an enhanced efficiency of the magnetron.