. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. SINE WAVE OSCILLATORS point at which to introduce them. They are a means of generating an exceed- ingly brief pulse, say, less than 1 microsecond, or they may be used to generate approximately triangular waves. Suppose we take an ordinary LC oscillator of the type first discussed and transpose the pick-up coil and the stabilizing RC network, as shown in Figure This has no effect on the operation of ^f T+. Figure Figure the circuit. Now suppose we increase CR. The time ta
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. SINE WAVE OSCILLATORS point at which to introduce them. They are a means of generating an exceed- ingly brief pulse, say, less than 1 microsecond, or they may be used to generate approximately triangular waves. Suppose we take an ordinary LC oscillator of the type first discussed and transpose the pick-up coil and the stabilizing RC network, as shown in Figure This has no effect on the operation of ^f T+. Figure Figure the circuit. Now suppose we increase CR. The time taken for the bias to adjust itself to a small reduction in the loop gain, perhaps caused by a small decrease in the HT supply, becomes longer till a stage is reached at which the oscillations apparently die away spontaneously. If now, to counteract this, we increase the loop gain, usually by increasing M, we find the amplitudes of oscillations become themselves oscillatory. Oscillations die away as before, then the bias leaks away, whereupon fierce oscillation becomes once more possible. Oscillations rapidly build up, generating a bias which eventually rises to a level too high to sustain them, then they die away once more (Figure ). This state of affairs is called 'squegging' and is the halfway house to the production of a blocking oscillator. To achieve the latter we go on increasing the loop gain, and the effect of this is to cause the oscillations to grow so fast that the capacitance is charged extremely quickly. Eventually a state is reached where the valve is cut off after only half a cycle of oscillation: this is the blocking oscillator. In that half-cycle enough grid current flows to charge the capacitor to a bias voltage which will prevent a further cycle of oscillation. The circuit is quiescent until this bias voltage has leaked away sufficiently for oscillation to recommence. The waveform across R and C Anode potential T Potential at top of /?and C. Please note t
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