Stabilized Feedback Oscillators

The author presents a mathematical consideration of the conditions which insure constant frequency of the vacuum tube oscillator under changes of electrode potentials or of the cathode temperature. It has already been shown that the grid and plate resistances may enter into the determination of the frequency. The problem is treated here in the manner suggested in the recent studies of feedback amplifiers. The conditions necessary for stability are developed in terms which are independent of particular circuit configurations and are applicable to certain dissipative circuits as well as to purely reactive systems. HE frequency deviations that accompany changes of the electrode potentials or of the cathode temperature in many types of vacuum tube oscillators have been recognized for some time as having their origin in the variation of the internal resistances of the tube. Llewellyn has shown 1 that both the grid and plate resistances may enter into the determination of the frequency and, by treating the problem as one of network design, has demonstrated the possibility of making the frequency substantially independent of the tube resistances. He also devised a large number of oscillator circuits stabilized in this way and established the conditions necessary for stabilization in each case. The problem is treated here in a somewhat more general manner suggested by recent studies of feedback amplifiers.2 The conditions necessary for stability are developed in terms which are independent of particular circuit configurations and which permit their application to certain types of dissipative circuits as well as to purely reactive systems.