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In electronics, the dynatron oscillator, invented in 1918 by Albert Hull at General Electric, is an obsolete vacuum tube electronic oscillator circuit which uses a negative resistance characteristic in early tetrode vacuum tubes, caused by a process called secondary emission.〔 on Peter Millet's (Tubebooks ) website〕 It was the first negative resistance vacuum tube oscillator. The dynatron oscillator circuit was used to a limited extent as beat frequency oscillators (BFOs), and local oscillators in vacuum tube radio receivers as well as in scientific and test equipment from the 1920s to the 1940s but became obsolete around World War 2 due to the variability of secondary emission in tubes. Negative transconductance oscillators,〔 such as the transitron oscillator invented by Cleto Brunetti in 1939, are similar negative resistance vacuum tube oscillator circuits which are based on negative transconductance (a fall in current through one grid electrode caused by an increase in voltage on a second grid) in a pentode or other multigrid vacuum tube.〔〔( Gottlieb, 1997, ''Practical Oscillator Handbook'', p. 78-81 )〕 These replaced the dynatron circuit〔 and were employed in vacuum tube electronic equipment through the 1970s.〔〔〔 ==How they work== The dynatron and transitron oscillators differ from many oscillator circuits in that they do not use feedback to generate oscillations, but negative resistance.〔〔 A tuned circuit (resonant circuit), consisting of an inductor and capacitor connected together, can store electric energy in the form of oscillating currents, "ringing" analogously to a tuning fork. If a tuned circuit could have zero electrical resistance, once oscillations were started it would function as an oscillator, producing a continuous sine wave. But because of the inevitable resistance inherent in actual circuits, without an external source of power the energy in the oscillating current is dissipated as heat in the resistance, and any oscillations decay to zero.〔 In the dynatron and transitron circuits, a vacuum tube is biased so that one of its electrodes has negative differential resistance.〔〔 This means that when the voltage on the electrode with respect to the cathode is increased, the current through it decreases.〔 A tuned circuit is connected between the electrode and the cathode. The negative resistance of the tube cancels the positive resistance of the tuned circuit, creating in effect a tuned circuit with zero AC resistance.〔〔 A spontaneous continuous sinusoidal oscillating voltage is generated, started by electrical noise in the circuit when it is turned on.〔 An advantage of these oscillators was that the negative resistance effect was largely independent of frequency, so by using suitable values of inductance and capacitance in the tuned circuit they could operate over a wide frequency range, from a few hertz to around 20 MHz.〔〔〔 Another advantage was that they used a simple single LC tuned circuit without the taps or "tickler" coils required by oscillators such as the Hartley or Armstrong circuits.〔 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「dynatron oscillator」の詳細全文を読む スポンサード リンク
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