- published: 18 Sep 2008
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In electronics, a vacuum tube, electron tube (in North America), thermionic valve, tube or valve is a device controlling electric current through a vacuum in a sealed container. The container is often thin transparent glass in a roughly cylindrical shape. Within the glass is a vacuum with a cathode and anode at either end. Electrons flow from the cathode to the anode through the vacuum, a demonstration of the Edison effect. The introduction of a grid between the cathode and anode makes it possible to amplify a current. A negative voltage applied to the grid will subdue the current traveling between cathode and anode through the vacuum by a larger value than the current applied to the grid. Hence the grid may be used to modulate the current through the tube.
Vacuum tubes are used for rectification, amplification, switching, or similar processing or creation of electrical signals. Tubes rely on thermionic emission of electrons from a hot filament or hot cathode. Electrons travel to the anode (or plate) when it is at a positive voltage with respect to the cathode. Additional electrodes between the cathode and anode regulate current, allowing a tube to amplify or to switch.