Vacuum tube
device that controls electric current between electrodes in an evacuated container
A vacuum tube, vac tube, electron tube, thermionic valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. It takes the form of an evacuated tubular envelope of glass or sometimes metal containing electrodes connected to external connection pins.
The type known as a thermionic tube or thermionic valve utilizes thermionic emission of electrons from a hot cathode for fundamental electronic functions such as signal amplification and current rectification. Non-thermionic types such as vacuum phototubes achieve electron emission through the photoelectric effect, and are used for such purposes as the detection of light and measurement of its intensity. In both types the electrons are accelerated from the cathode to the anode by the electric field in the tube.
The first, and simplest, vacuum tube, the diode or Fleming valve, was invented in 1904 by John Ambrose Fleming. It contains only a heated electron-emitting cathode and an anode. Conventional current can flow in only one direction through the device: from the cathode to the anode (hence the name "valve", like a device permitting one-way flow of water). Adding one or more control grids within the tube, creating the triode, tetrode, etc., allows the current between the cathode and anode to be controlled by the voltage on the grids, creating devices able to amplify as well as rectify electric signals. Multiple grids (e.g., a heptode) allow signals applied to different electrodes to be mixed.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Sep 15, 2026. The linked authority identifier is Q3574371. The Library of Congress control number is sh85141746. None of the 1 selected statements returned an explicit reference. The first chronological checks are 1904.
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This entry incorporates text from “Vacuum tube” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.