. Electronic apparatus for biological research . HT-t (a) (b) Figure Arrangements for maintaining the level of oscillation have to be more elaborate than the simple self-biasing device which is adequate for LC oscillators. This is because the RC frequency-determining networks have of themselves only a very small Q value; one could not possibly tolerate the pulsatory currents which are permissible in LC oscillators because there is no device with a g of several hundred to re-create a pure sine waveform. Thus the valves must amphfy in class A, without distortion, and some other means must

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. Electronic apparatus for biological research . HT-t (a) (b) Figure Arrangements for maintaining the level of oscillation have to be more elaborate than the simple self-biasing device which is adequate for LC oscillators. This is because the RC frequency-determining networks have of themselves only a very small Q value; one could not possibly tolerate the pulsatory currents which are permissible in LC oscillators because there is no device with a g of several hundred to re-create a pure sine waveform. Thus the valves must amphfy in class A, without distortion, and some other means must be found of regulating the gain. D'Argidmbeau's method—There is a variety of pentode known as 'variable fi' {Figure ). As a result of grading the mesh size of the control grid along the axis of the valve it can be shown that the ampHfication obtainable from the valve is a function of the mean grid bias {Figure ). Clearly if the

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