This tag is for questions relevant to vacuum tubes, also known as thermionic valves or simply valves.

Despite having gained the moniker "glow-FET", a vacuum tube is century-old technology in which electron flow is manipulated and controlled by grids, beam forming plates. The first vacuum diodes (rectifiers and detectors) appeared in 1907, and by 1914 they were widely used in radio, both commercial transmitters and high-end receivers. They figured heavily in science fiction as late as the 1960s, despite already beginning to be replaced by transistors for most applications.