Frequency variations in thermionic generators

Abstract
The paper is divided into six parts, as follows:-In Part I the variations of frequency which occur in mechanical oscillating systems with pendulum control are referred to. Unless the driving impulses are given at the moment the pendulum is vertical, the frequency of the oscillations varies from the true oscillation frequency of the pendulum. When the pendulum is near the limit of its swing an impulse directed inwards makes the clock go fast, whilst an impulse directed outwards makes the clock go slow. Such an effect is “reversible” because the clock goes fast or slow according to the direction in which the impulse is applied. Another type of variation is connected with the amplitude of the swing, and makes its appearance unless the amplitude is infinitesimal. Increase of amplitude always makes the clock go slow, and the effect is therefore “irreversible”In Part II the phase relationships of currents and potentials in a thermionic generator arc examined, and it is shown that the frequency of the oscillations is affected by the nature of the coupling between the grid and anode circuits. Equations are obtained which give the difference between the frequency of the oscillations generated and the resonant frequency of the tuned circuits. These equations show that the variations of frequency connected with the method of coupling are analogous to the reversible variations existing in the pendulum-controlled clock. With normal coupling the thermionic generator goes slow, with reversed coupling it goes fast, and with resistance coupling the variation disappears.In Part III three “irreversible” variations of frequency are discussed, namely :-(i) A variation connected with a change in the effective inductance of the circuit, which occurs when the oscillation is free instead of forced;(ii) A variation connected with a change in the resonant frequency of a damped circuit, which occurs when the oscillation is free instead of forced; and(iii) A variation associated with the presence of harmonics in the E.M.F. generated by the valve.In Part IV certain points in the design of thermiornic generators employing resistance coupling are discussed.In Part V the design of thermionic generators using reversed coupling is discussed, and some interesting points affecting the design of untuned circuits are described.In Part VI the experimental results obtained with various types of circuit are given, and are explained in terms of the theoretical variations discussed in Parts II and III.The characteristics of various types of constant-frequency generator are then compared. It is pointed out that frequency variations associated with changes in the voltage of supply can be reduced below 1 part in 20 000, or 1 part in 50 000, according to circumstances.

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