Gas tube

(electronics) An electron tube into which a small amount of gas or vapor is admitted after the tube has been evacuated; ionization of gas molecules during operation greatly increases current flow.

An electron tube that contains gas or vapor at low pressure in which an electrical discharge takes place. Gas tubes are of two general types: cold-cathode tubes, in which the phenomenon known as glow discharge serves to maintain a conducting path between the electrodes, and hot-cathode tubes, in which an arc discharge conducts the current. The cold-cathode glow tubes are characterized by a relatively high voltage drop and a low current, while the hot-cathode arc tubes are characterized by a low voltage drop and relatively high current. See also Electron tube.

Cold-cathode gas tubes, or glow tubes, require no cathode heater power and are therefore always ready for instant service. Glow tubes are commonly constructed as two-element (diode) or three-element (triode) tubes.

Three representative types of hot-cathode gas tubes may be distinguished: the Tungar (sometimes called a Rectigon), the phanotron, and the thyratron. The first two are simple rectifier tubes while the third is a control tube having one or two grids between cathode and anode. Both phanotrons and thyratrons may be built with glass, ceramic, or metal envelopes.