Vacuum Tube Oscillators-A Graphical Method of Analysis

T HE vacuum tube oscillator is fast becoming one of our most versatile circuits and the requirements which are being imposed upon it are constantly increasing in severity. In some cases it is asked to efficiently convert several kilowatts of direct current power to alternating current power. At other times, it may be called upon to deliver an alternating current having a frequency which shall remain constant within extremely narrow limits. It may be required to operate at a few cycles per second or at several million. The question of frequency stability has recently taken on considerable importance. The need for currents of accurately known frequency is being felt in all branches of the electrical communication art, particularly in the field of multiplex transmission over wires by means of carrier currents and in radio broadcasting. The factors affecting the frequency of an oscillator will for this reason be given attention in the following discussion. The operation of a vacuum tube oscillator or, in fact, of any system maintained in continuous oscillation, has certain unique features. In order for such a system to be in stable equilibrium its several elements must adjust themselves until certain necessary conditions are established. It is important, in an analytical study of oscillators, to know the manner in which this adjustment takes place. If any operating condition may be defined by an equation made up of independent variables, it is a relatively simple matter to predict the result of changes in a single one.