(Russian, elektrovakuumnyl pribor), a device that is used to generate, amplify, or convert electromagnetic energy and whose operating cavity is air-free and is protected from the ambient air by a rigid, gastight envelope. Electro-tube devices include incandescent lamps, vacuum-tube devices (in which electrons move in a vacuum), and gas-discharge devices (in which electrons flow in a gas).
Incandescent lamps. Incandescent lamps are the most widely used type of electron-tube device; approximately 10 billion were produced annually throughout the world in the 1970’s. The evacuation of air from the bulb of an incandescent lamp prevents oxidation of the lamp’s filament. In order to reduce vaporization of the filament, some types of incandescent lamp are filled with an inert gas after the air has been evacuated. This enables the filament to operate at a higher temperature and increases the luminous efficacy without diminishing the lamps’ service life. The presence of the inert gas does not affect the conversion into light of the electric energy supplied to the lamp.
Vacuum-tube devices. Vacuum-tube devices are fabricated in such a way that the pressure of residual gases within the envelope ranges from 10–6 mm to 10–10 mm of mercury when the tube is operating. With this degree of rarefaction, the ions of the residual gases do not influence electron trajectories, and the noise generated by the flow of the ions to the cathode is fairly low.
Vacuum-tube devices include multielement tubes, microwave tubes, electron-beam instruments, photoelectric devices, vacuum-tube indicators, and X-ray tubes.
Multielement vacuum tubes, such as triodes, tetrodes, and pentodes, are designed to convert direct current into electric oscillations at frequencies of up to 3 x 109 hertz (Hz). The principal fields of application of multielement tubes are radio engineering, radio communications, radio broadcasting, and television.
Microwave tubes include magnetrons and magnetron-type devices, multiresonator and reflex klystrons, and traveling-wave and backward-wave tubes. Designed to convert direct current into electromagnetic oscillations at frequencies ranging from 3 x 108 Hz to 3 x 1012 Hz, they are used primarily in radar, television (for the transmission of television signals along radio-relay links and satellite links), microwave communications, and remote control of, for example, satellites and space vehicles.
Electron-beam devices include oscillograph tubes, picture tubes, and storage tubes. Such devices are employed in the conversion of information that exists in the form of electric or light signals. They may be used, for example, to produce visual representations of electric signals or to convert two-dimensional visual images into a succession of television signals and vice versa.
Photoelectric devices, which include camera tubes, photomultipliers, and phototubes, convert light energy into an electric current. Photoelectric devices are used in automatic equipment as well as in equipment employed in, for example, television, astronomy, nuclear physics, sound motion pictures, and facsimile.
Vacuum-tube indicators include cathode-ray tuning indicators and numerical indicator tubes. Indicator tubes convert direct current into light energy. Among their applications are measuring instruments, display devices, and radio receivers.
X-ray tubes, which convert direct current into X rays, are employed in the field of medicine to diagnose certain illnesses. X-ray tubes are used in industry to detect internal flaws of products and in physics and chemistry to determine the structure and parameters of crystal lattices in solids, the chemical composition of substances, and the structure of organic substances. X-ray tubes are also used in biology to determine the structure of complex molecules.
Gas-discharge devices. The gas pressure in gas-discharge, or ion, devices is usually substantially lower than atmospheric pressure. Gas-discharge devices include high-power gas-filled devices, discharge lamps, pulsed-light sources, gas-discharge indicators, and quantum gas devices.
High-power devices, whose operation is based on space-charge neutralization by gas ions, can handle as much as several megawatts of power at currents of thousands of amperes. They include mercury-arc rectifiers, which are used in such areas as industry and railroad transportation to convert alternating current to direct current; pulse-forming hydrogen thyratrons and tacitrons, which convert direct current into pulses in, for example, radar equipment and equipment used in electron discharge machining; and spark dischargers and clipper devices, which are used to protect equipment from overvoltages.
Continuous discharge lamps are used for lighting interior spaces and streets. Other applications include illuminated signs and movie-projection equipment. Among the applications of pulsed-light sources are automation devices, remote-control devices, and equipment associated with data transmission and optical detection and ranging.
Gas-discharge indicators may be signal indicators, character displays, or linear-and matrix-type displays. They are used for the visual representation of information in, for example, computers.
Quantum gas devices, which convert direct current into coherent radiation, include gas lasers and quantum frequency standards.
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V. F. KOVALENKO