Cutaway diagram of a triode vacuum tube, showing the plate (anode)
In electronics, a plate, usually called anode in Britain, is a type of electrode that forms part of a vacuum tube. It is usually made of sheet metal, connected to a wire which passes through the glass envelope of the tube to a terminal in the base of the tube, were it is connected to the external circuit. The plate is given a positive potential, and its function is to attract and capture the electrons emitted by the cathode. Although it is sometimes a flat plate, it is more often in the shape of a cylinder or flat open-ended box surrounding the other electrodes.
The plate must dissipate heat created when the electrons hit it with a high velocity after being accelerated by the voltage between the plate and cathode. Most of the waste power used in a vacuum tube is dissipated as heat by the plate. In low power tubes it is usually given a black coating, and often has "fins" to help it radiate heat. In power vacuum tubes used in radio transmitters it is often made of a refractory metal like molybdenum. and is part of a large heat sink that projects through the glass or ceramic tube envelope and is cooled by forced air or water.