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Circlotron valve amplifier is a type of power amplifier utilizing symmetrical cathode-coupled bridge layout of the output stage. Original circlotrons of 1950s used output transformers to couple relatively high output impedance of vacuum tubes to low-impedance loudspeakers. Circlotron architecture, easily scalable, was eventually adapted to operate without output transformers, and present-day commercially produced circlotron models are of output transformerless (OTL) type. == History == The ''Circlotron'' name emerged as a trademark of Electro-Voice. A U.S. patent for a circlotron ''High Fidelity Audio Amplifier'' was filed by Alpha Wiggins of Electro-Voice on March 1, 1954, and granted March 28, 1958.〔U.S. Patent 2,828,369〕 However, other inventors filed the same concept earlier:〔(circlotron.tripod.com )〕 * C. T. Hall filed ''Parallel Opposed Power Amplifiers'' on June 7, 1951; U.S. Patent 2,705,265 was granted on March 29, 1955. * Tapio Köykkä filed on September 2, 1952; Finnish Patent 27332 granted on November 10, 1954; improved version was filed on September 30, 1955, Finnish Patent 29642 granted on April 10, 1958. All these patents called for a transformer-coupled, fully balanced design; commercial transformerless amplifiers were not feasible at this time due to high costs of power supply capacitors required for an OTL design (at least thousands of microfarads at 200 volts or better). In the 1950s and 1960s, circlotrons were produced by Electro-Voice (eight models, 15 to 100 watts per channel), Finnish Voima and Philips.〔 These inspired other local manufacturers, such as Carad. All these models employed output transformers and beam tetrode or pentode tubes (for increased efficiency). Similar amateur designs were published in the USSR. One can observe that the output stage of the successful McIntosh amplifier is a circlotron too because the special winding of the output transformer eliminates one of the two floating power supplies. The concept was resurrected in its transformerless form in early 1980s by Ralph Karsten, founder of Atma-Sphere, which remains the principal contemporary manufacturer of circlotrons. Other OTL circlotrons were made by Tenor Audio, Joule Electra and Einstein. 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「Circlotron」の詳細全文を読む スポンサード リンク
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