A predecessor of solid state electronics. An electron tube evacuated sufficiently high to allow electrons to move with low interaction with remaining molecules of air or gas.
Although they have been largely replaced by solid state electronics, vacuum tubes of interest to the welding industry are the thyratron, which changes alternating current into direct current and regulates the flow, and the ignitron, which also changes high-voltage alternating current into direct current. The ignitron depends on the presence of liquid mercury inside the tube. Some tubes, such as the ignitron, are housed in large tanks which have running water to cool parts of the tube because of the high heats that are generated. See ELECTRONIC TUBE.