Vacuum Tube

An electron tube evacuated to such a degree that its electrical characteristics are essentially unaffected by the presence of residual gas or vapour.

Historical Notes

  1. 1904 first tube, a two-element diode, invented and patented by Ambrose Fleming
  2. 1907 Lee de Forest developed the first triode by adding a grid between the cathode and the anode, this was the first amplifier.


That electrode within a tube which is heated for electron emission or which transfers its heat to a separate cathode for electron emission.

Indirectly-heated Tube

A tube in which the filament heats the cathode to produce electron emission.

Interelectrode Capacity

The internal capacitances existing between the elements of a vacuum tube.

See also: Cathode Ray Tube, Filament, Ignitron, Pentagrid Converter.

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Subjects: Physics