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A magic eye indicator, called in technical literature an electron-ray indicator tube, is a vacuum tube which gives a visual indication of the strength of an electronic signal, such as an audio output, radio-frequency signal strength, or other functions.〔 It is also called a cat's eye, or tuning eye in America. Its first broad application was as a tuning indicator in radio receivers, to give an indication of the relative strength of the received radio signal, to show when a radio station was properly tuned in.〔 The eye tubes were developed as a cheaper alternative to the needle movement meters. It was not until the 1960s that needle meters were made economically enough in Japan to displace indicator tubes.〔http://home.comcast.net/~jlrmsousa/precise_db_monitoring_with_eye_tubes_november_2006_audioxpress_joe_sousa2667.pdf〕 The tubes were used in vacuum tube receivers from around 1936 to 1980 before vacuum tubes were replaced by transistors in radios. An earlier tuning aid which the Magic Eye replaced was the "Tuneon" neon lamp.〔〔(Radio Museum: Tuneon )〕 ==History== The "magic eye" valve for tuning radio receivers was invented in 1932 by Allen B. DuMont (who spent most of the 1930s improving the lifetime of cathode ray tubes, and ultimately formed the DuMont Television Network).〔David Weinstein, ''The Forgotten Network: DuMont and the Birth of American Television''. Temple University Press, 2006, p.11〕 It is a miniature cathode ray tube, usually with a built-in triode signal amplifier. It usually glows bright green, (occasionally yellow in some very old types, e.g., EM4) and the glowing ends grow to meet in the middle as the voltage on a control grid increases. It is used in a circuit that drives the grid with a voltage that changes with signal strength; as the tuning knob is turned, the gap in the eye becomes narrowest when a station is tuned in correctly. The RCA 6E5 of 1935 was the first commercial tube.〔Herbert M. Wagner of R.C.A. invented the familiar form of the "magic eye" tuning vacuum tube: 〕〔(Radio Museum: 6E5 )〕 These devices were basically made in two forms – an end-viewed type usually with an octal or side-contact base, and a smaller side-viewed noval B9A based all-glass type. The round cone-shaped fluorescent screen together with the black cap that shielded the red light from the cathode/heater assembly was what prompted the contemporary advertisers to coin the term "Magic Eye", a term still used. There was a miniature version with wire ends (Mullard DM70/DM71, Mazda 1M1/1M3, GEC/Marconi Y25) intended for battery operation, used in one Ever Ready AM/FM battery receiver with push-pull output, as well as a small number of AM/FM mains receivers, which lit the valve from the 6.3V heater supply via a 220-ohm resistor or from the audio output valve's cathode bias. It is more like a modern Vacuum fluorescent display than a CRT. One or two small reel-to-reel tape recorders also used the DM70/DM71 to indicate recording level, including a transistorised model with the valve lit from the bias-oscillator voltage. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Magic eye tube」の詳細全文を読む スポンサード リンク
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