vacuum tube

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Electron tube consisting of a sealed glass or metal enclosure from which the air has been withdrawn.

It was used in early electronic circuitry to control a flow of electrons. In the first half of the 20th century, vacuum tubes allowed the development of radio broadcasting, long-distance telephone service, television, and the first electronic digital computers, which were the largest vacuum-tube systems ever built. Transistors have replaced them in virtually all applications, but they are still occasionally used in display devices for television sets and computers (cathode-ray tubes), in microwave ovens, and as high-frequency transmitters on space satellites.

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glass: preparation of graded-index optical fibre

More on "vacuum tube" from Britannica Concise:

cathode-ray tube - Vacuum tube that produces images when its phosphorescent surface is struck by electron beams.

Audion - Elementary radio tube developed by Lee De Forest (patented 1907).

amplifier - Device that responds to a small input signal (voltage, current, or power) and delivers a larger output signal with the same waveform features.

ENIAC - Early electronic digital computer built in the U.S. in 1945 by J. Presper Eckert and John W. Mauchly.

radio - Electromagnetic radiation of lower frequency (hence longer wavelength) than visible light or infrared radiation, and consisting of the range of frequencies used for navigation signals, AM and FM broadcasting, television transmissions, cell-phone communications, and various forms of radar.

More on "vacuum tube" from the 32 Volume Encyclopædia Britannica:

electron tube - device usually consisting of a sealed glass or metal-ceramic enclosure that is used in electronic circuitry to control a flow of electrons. Among the common applications of vacuum tubes are amplification of a weak current, rectification of an alternating current (AC) to direct current (DC), generation of oscillating radio-frequency (RF) power for radio and radar, and creation of images on a ...

vacuum technology - all processes and physical measurements carried out under conditions of below-normal atmospheric pressure. A process or physical measurement is generally performed in a vacuum for one of the following reasons: (1) to remove the constituents of the atmosphere that could cause a physical or chemical reaction during the process (e.g., vacuum melting of reactive metals such as titanium); (2) to ...

electronics - Theoretical and experimental studies of electricity during the 18th and 19th centuries led to the development of the first electrical machines and the beginning of the widespread use of electricity. The history of electronics began to evolve separately from that of electricity late in the 19th century with the identification of the electron by the English physicist Sir Joseph John Thomson and the ...

radio - An electron tube or transistor, designated an active element, functions basically as an amplifier, and its output is essentially an amplified copy of the original input signal. The simplest amplifying electron tube is the triode, consisting of a cathode coated with material that provides a copious supply of electrons when heated, an open-mesh grid allowing electrons to pass through but ...

electron tube - An electron tube has two or more electrodes separated either by vacuum (in a vacuum tube) or by ionized gas at low pressure (in a gas tube). Its operation depends on the generation and transfer of electrons through the tube from one electrode to another. The source of electrons is the cathode, usually a metallic electrode that releases a stream of electrons (see ) by one of several mechanisms ...

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