The Van Der Pol Four-Electrode Tube Relaxation Oscillation Circuit

Relaxation oscillations of an electrical nature are defined, and the operation of a tetrode relaxation circuit is described in detail. The mechanism of frequency division is explained, and oscillograms of the oscillations in this circuit are shown, both of the free oscillation and of the oscillation as controlled in frequency division. The characteristics of the oscillator are discussed with reference to frequency drift and stability of frequency division. The period of the oscillator is shown to be approximately RC log V
1
/V
2
, where V
1
and V
2
are initial and final voltages on the condenser, respectively, during the discharge. V
1
/V
2
is shown to change very steeply with average internal grid resistance. Modifications are shown for increasing the frequency stability and over-all efficiency of the system, and for controlling the ratio of charging time to discharging time of the condenser. A further modification is suggested for making the internal grid resistance independent of filament voltage when the grid is positive.