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The Audion was an electronic amplifying vacuum tube〔 invented by American electrical engineer Lee De Forest in 1906.〔De Forest patented a number of variations of his detector tubes starting in 1906. The patent that most clearly covers the Audion is , ''(Space Telegraphy )'', filed January 29, 1907, issued February 18, 1908〕〔 The link is to a reprint of the paper in the ''Scientific American Supplement, No. 1665, November 30, 1907, p.348-350, copied on Thomas H. White's (United States Early Radio History ) website〕 It was the first triode, consisting of a partially evacuated glass tube containing three electrodes; a heated filament, a grid, and a plate.〔 It is important in the history of technology because it was the first widely used electrical device which could amplify; a small electrical signal applied to the grid could control a larger current flowing from the filament to plate.〔〔 Unlike later vacuum tubes, the primitive Audion had a small amount of gas in the tube, thought to be necessary by De Forest, which limited the dynamic range and gave it nonlinear characteristics and erratic performance.〔〔 Originally developed as a radio receiver detector〔 by adding a grid electrode to the Fleming valve, it found little use until its amplifying ability was recognized around 1912 by several researchers,〔 who used it to build the first amplifying radio receivers and electronic oscillators.〔〔. Republished as 〕 The many practical applications for amplification motivated its rapid development, and the original Audion was superseded within a few years by improved versions with higher vacuum, developed by Irving Langmuir at GE and others.〔〔 These were the first modern "hard vacuum" triodes.〔 == History == It had been known since the middle of the 19th century that gas flames were electrically conductive, and early wireless experimenters had noticed that this conductivity was affected by the presence of radio waves. De Forest found that gas in a partial vacuum heated by a conventional lamp filament behaved much the same way, and that if a wire were wrapped around the glass housing, the device could serve as a detector of radio signals. In his original design, a small metal plate was sealed into the lamp housing, and this was connected to the positive terminal of a 22 volt battery via a pair of headphones, the negative terminal being connected to one side of the lamp filament. When wireless signals were applied to the wire wrapped around the outside of the glass, they caused disturbances in the current which produced sounds in the headphones. This was a significant development as existing commercial wireless systems were heavily protected by patents; a new type of detector would allow De Forest to market his own system. He eventually discovered that connecting the antenna circuit to a third electrode placed directly in the current path greatly improved the sensitivity; in his earliest versions, this was simply a piece of wire bent into the shape of a grid-iron (hence "grid"). Compared to all competing devices at the time, the Audion was unique in that it did not draw significant power from antenna/tuned circuit, which allowed the tuning circuitry to operate with maximum selectivity. With virtually all other systems, all of the power to operate the headphones had to come from the antenna circuit itself, which tended to "damp" the tuned circuits, limiting their ability to separate stations (distinguish discrete frequencies). 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「Audion」の詳細全文を読む スポンサード リンク
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