In honor of the coverage of cavity-magnetron history in this issue, here ia a classic: the 4J50. This device, with its built-in magnet, was designed by Bell Labs for manufacture by Western Electric during WWII, but successful enough to be offered by at least eight other makers in the US, Britian, the Netherlands, France and Germany for many years. This illustration is art from Philips as of 1962. The tube put out pulses of 225kW at 9375 MHz to 30 MHz. A varient, the 4J78, ran at 9085 MHz.