Minimizing the Effect of Cutoff in TV Vertical Oscillators

The vertical oscillator of a TV set, whether a multivibrator or a blocking oscillator, can be very dependent upon the cutoff characteristic of the tube. It can affect the speed or frequency of the oscillator, the linearity and the synchronizing characteristic. There are several classes of cutoff current of the tube, namely that which is controlled by the grid voltage and that which is uncontrolled or ``dead´´ plate current. Both of these have different effects on the performance of the circuit and tube. Some circuits are sensitive to cutoff currents as low as 10-4 times the peak current drawn during the cycle. Circuits can be modified to mitigate the effect of tube cutoff and several ways of doing this are described in the paper.