Electron Tube

Electron Tube, any of a wide range of electronic devices used to control electric currents and to manipulate electric signals in some way. They are devices of the 20th century; the first such tube—the diode—having been invented in 1905.

Electron tubes consist basically of a metal, ceramic, or glass tube, evacuated of air to some degree or filled with a gas such as mercury vapor, and incorporating two or more electrodes (see Electrode). One of the electrodes, the cathode, must be heated in order to provide the stream of electrons needed for the electron tube to function. These devices are used in electronic circuitry, radio and television, and radar installations; and they have a large number of research and industrial applications. For some uses electron tubes have been replaced by solid-state devices such as the transistor, which take up less space, use lower voltages, and do not need a heated cathode. For uses requiring high power, however, electron tubes remain essential.

See also Cathode.Ray Tube; Electronics; Microwaves; Oscilloscope; Photoelectric Cell; Television; Vacuum Tubes; X Ray.