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A pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid amplifying vacuum tube (thermionic valve), which was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926.〔G. Holst and B.D.H. Tellegen, "Means for amplifying electrical oscillations", US Patent 1945040, January 1934.〕 The pentode consists of an evacuated glass envelope containing five electrodes in this order: a ''cathode'' heated by a filament, a ''control grid'', a ''screen grid'', a ''suppressor grid'', and a ''plate'' (anode). The pentode (called a "triple-grid amplifier" in some early literature〔"RCA Receiving Tube Manual, 1940"; p118〕) was developed from the tetrode tube by the addition of a third grid, the suppressor grid. This served to prevent secondary emission electrons emitted by the plate from reaching the screen grid, which caused instability and parasitic oscillations in the tetrode. The pentode is closely related to the beam tetrode. Pentodes were widely used in industrial and consumer electronic equipment such as radios and televisions until the 1960s, when they were replaced by transistors. Their main use now is in high power industrial applications such as radio transmitters. The obsolete consumer tubes are still used in a few legacy and specialty vacuum tube audio devices. == Types of pentodes == * Variable transconductance ("variable-mu", "remote-cutoff" or "super-control") tubes in general are those with a non-uniform grid wire spacing to allow them to handle a wide range of input signal levels without excessive cross-modulation distortion, and so useful in radio frequency stages where automatic gain control is applied to the pentode. The first commercial variable-mu tubes were the 550 and 551 developed by Stuart and Snow around 1929.〔Stuart, B & Snow, H. A. (1930). Reduction of Distortion and Cross-Talk in Radio Receivers by Mean of Variable-Mu Tetrodes. Proc IRE, Vol 18, Issue 12, pp2102 - 2127〕 Other examples include: EF50, 1T4, 6K7, 6BA6, and the EF83 (while perhaps the EF85/6BY7, and certainly the 6JH6, could be described as "semiremote-cutoff" pentodes). * Sharp-cutoff ("high slope" or ordinary) pentodes have the more ordinary uniform spacing of grid wires, and so mutual conductance decreases in an essentially uniform manner with increasing negative bias, and has a more abrupt cutoff. These pentodes are more suitable for audio amplifiers. Examples include: EF37A, EF86/6267, 1N5GT, 6AU6A, 6J7GT. Often, but not always, in the European valve naming scheme for pentodes an even number indicated a sharp-cutoff device while odd indicated remote-cutoff; the EF37 was an exception to this general trend, perhaps due to its history as an update to the EF36 (("The Mullard EF36, EF37 and EF37A" at the National Valve Museum )). * Power output pentodes, The EL34, EL84, 6CL6, 6F6, 6G6, SY4307A and 6K6GT are some examples of true pentodes used for power amplification, using a suppressor grid rather than the higher efficiency beam-forming plates used in beam tetrodes. (Beam tetrodes were also sometimes referred to as "beam pentodes",〔"Sylvania Receiving Tubes Technical Manual, 14th Edition" p 143〕 and include the Sylvania (and possibly GE) 6CA7 version of EL34, 6V6GT and the GEC KT66 and KT88. Other sources perferred names such as "beam power amplifier" or "beam power tube", possibly due to caution regarding the Philips pentode patent). Power output pentodes for specific television requirements, efficient for their job but possibly not linear enough for audio, were named: * * video output pentodes, e.g. 15A6/PL83, PL802 * * frame output or vertical deflection pentodes, such as the PL84 and the pentode sections of the 18GV8/PCL85. * * line output or horizontal deflection pentodes, such as the PL36, 27GB5/PL500, PL505 etc. * A "triode-pentode" is a single envelope containing both a triode and a pentode, such as an ECF80 or ECL86. 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「Pentode」の詳細全文を読む スポンサード リンク
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