Vacuum tube

An electronic device that controls the flow of electrons through an evacuated enclosure. Vacuum tubes can amplify signals, switch circuits, or convert alternating current to direct current.

Thermionic emission: The release of electrons from a heated material into a surrounding vacuum or gas. Heated cathodes supply the electrons that vacuum tubes control.
Anode: An electrode at which oxidation occurs in an electrochemical cell; in a vacuum tube, the electron-collecting electrode. Tube diagrams often call the electron-collecting electrode the anode or plate.
Edison effect: The observation that current can flow from a heated filament to a nearby electrode inside an evacuated bulb. This effect revealed thermionic emission and inspired early valve experiments.
Radio receiver: An electronic device that selects and processes radio signals to recover transmitted information. Vacuum tubes amplified weak antenna signals and enabled early radio reception.
Vacuum diode: A two-electrode vacuum tube that permits substantial electron flow primarily in one direction. It is the simplest tube and illustrates rectification without a control grid.
Cathode: An electrode that emits or receives electrons, depending on the device and operating conditions. In a thermionic tube, the heated cathode is the electron source.
Plate current: The current flowing through a vacuum tube’s anode, commonly called its plate current. It is the output current controlled by the grid in an amplifying tube.
John Ambrose Fleming: An English electrical engineer who invented the two-electrode thermionic valve in 1904. Fleming turned the Edison effect into a practical rectifying device.
Vacuum-tube audio amplifier: An audio amplifier that uses vacuum tubes to increase the power of sound-frequency signals. Tube stages amplify audio and remain used in some musical and hi-fi equipment.
Bipolar junction transistor: A semiconductor device in which current through two terminals is controlled by current at a third terminal. It replaced many tube amplifiers and switches with smaller, lower-power components.

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