Definition
A thermionic tube, also known as a vacuum tube, is an electronic device that controls electric current between electrodes in an evacuated enclosure. It relies on thermionic emission, where heat causes electrons to be released from a hot cathode. These electrons are then manipulated by electric fields to amplify or switch signals. Thermionic tubes were fundamental to early electronics, serving as the basis for radios, TVs, and early computers. Although largely replaced by transistors, they remain relevant in some specialized applications. They are the predecessor to a modern microchip.