valve (electronics)

In electronics, a glass or metal tube containing gas at low pressure, which is used to control the flow of electricity in a circuit. The electron tube valve was developed by US radio engineer Lee de Forest (1873–1961) and is used to modify electrical signals. Three or more metal electrodes are inset into the tube. By varying the voltage on one of them, called the grid electrode, the current through the valve can be controlled, and the valve can act as an amplifier. It is called a valve because it allows a unidirectional flow of electrons.

Valves have been replaced for most applications by transistors. However, they are still used in high-power transmitters and amplifiers, and in some hi-fi systems.