Vacuum Tube Oscillators A Graphical 

 Method of Analysis 



By J. W. HORTON 



Introduction 



THE 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 con- 

 siderable 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 ele- 

 ments 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. When, however, a change in 

 one quantity is accompanied by a general readjustment of all the 

 others, it is quite difficult to obtain a clear picture of what occurs 

 from an equation. Graphical methods are better suited to a study 

 of the manner in which a number of inter-dependent variables arrive 

 at an equilibrium condition. Such a graphical treatment will be 

 described in the following paragraphs and its application to the 

 design of a circuit to perform certain specified duties will be discussed. 



Gr.M'HKAI, MkTHOU for DETliRMININO CONDITIONS 



OF Stable Oper.\tion 



It is sometimes convenient to think of an electrical transmission 

 system as being made up of a number of units, each deliveiing energy 



SOS 



