A miniature voltage-tunable O-type backward wave oscillator tube from 1956, manufactured by Varian Industries. The backward wave oscillator, invented in 1951 by Rudolf Klompfner, is a specialized linear-beam tube which generates microwaves. The accompanying ad copy says this tube can operate over an 8.2 - 12.4 GHz range with supply voltage of 300-600 V. The body is approximately 4 inches long. The magnet required for operation weighs less than 5 lbs. Alterations to image: Cropped out ad copy.