Also known as a valve, an evacuated glass or metal tube which may contain gas at low pressure, through which electrons flow between two or more electrodes. A heated filament, the cathode, emits electrons which are attracted to the positively-charged anode.
The diode, used for rectification, consists of a negative cathode, which emits electrons when heated, and a positive anode or plate. The triode, used for amplification, has a perforated control grid between the cathode and the anode; a signal fed to the grid provides an amplified signal at the anode.
Electron tubes have been largely replaced by transistors and other semiconductor devices.
Related categories ELECTRICITY AND MAGNETISM
ELECTRONICS AND SEMICONDUCTORS
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