Tube: 1B40 Posted By Radu Motisan on May 9, 2013 Pictures: Details: External Cavity, 1KW at 1075 to 1096MHz. ‘Electrodeless’ discharge: the tube has the ground ring and a keep-alive electrode connection in the base. Made by Bomac and Sylvania. It measures 38x20mm (12mm across glass). Datasheet: n/a Links: Radiomuseum Tubecollector Disk seal vacuum tubes