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Ultra-linear electronic circuits are those used to couple a tetrode or pentode vacuum tube (also called "electron valve") to a load (e.g. to a loudspeaker). 'Ultra-linear' is a special case of 'distributed-loading'; a circuit technique patented by Alan Blumlein in 1937 (Patent No. 496,883), although the name 'distributed-loading' is probably due to Mullard. In 1938 he applied for the US patent 2218902. The particular advantages of ultra-linear operation, and the name itself, were published by David Hafler and Herbert Keroes in the early 1950s through articles in the magazine "Audio Engineering" from the USA.〔.〕 The special case of 'ultra-linear' operation falls under the more general principle of 'distributed-loading'. ==Operation== A pentode or tetrode vacuum tube (electron valve) configured as a common-cathode amplifier (where the output signal appears on the plate) may be operated as: * a pentode or tetrode, in which the screen grid is connected to a stable DC voltage so there are no signal variations on the screen grid (i.e. the screen grid has 0% of the plate's output signal impressed on it), or * a triode, in which the screen grid is connected to the plate (i.e. the screen grid has 100% of the plate's output signal voltage impressed on it), or * a blend of triode and pentode, in which the screen grid has a percentage (between 0% and 100%) of the plate's output signal impressed on it. This is the basis of the ultra-linear circuit, and is usually achieved by incorporating a suitable "tap" on the primary winding of the output transformer that the vacuum tube (electron valve) is connected to. The impression of any portion of the output signal onto the screen grid (load distribution) can be seen as a form of feedback, which alters the behavior of the electron stream passing from cathode to anode. Among other benefits, this feedback helps to more accurately reflect the instantaneous reactance of the load (secondary circuit) back to the valves (primary circuit), thus offering better load-control and responsiveness (i.e. improved loudspeaker damping and power stability as load impedance varies across frequency band). 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「Ultra-linear」の詳細全文を読む スポンサード リンク
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