English: The first commercial klystron in 1940, manufactured by Westinghouse. Part of the tube is cut away to show the internal construction. The klystron, invented in 1937 by Russel and Sigurd Varian at Stanford University, is a linear beam vacuum tube which generates microwaves. It could generate 200 W of power at 40 centimeters (750 MHz) with 50% efficiency. On the left is the cathode and accelerating anode which creates the electron beam. In the center between the wooden supports is the drift tube, surrounded by the two donut-shaped cavity resonators, the "buncher" to which the input signal is applied, and the "catcher" from which the output signal is taken. The output terminal is visible at top. On the right is the cone shaped collector anode which absorbs the electrons.