STABILIZED FEEDBACK OSCILLATORS 467 



zero and the oscillation frequency stabilized when the elements are so 

 proportioned that 



LoCi = L2C3, (27) 



under which condition the oscillation frequency is determined by the 

 equation 



At the oscillation frequency the value of n^ (equation 10) becomes 

 /.^o = ^^^^ ^ (!9) 



and is equal to unity when 



Equation (30) can be used to determine the amplitude of the 

 stabilized oscillations if the variation of the resistance ratio with ampli- 

 tude is known or can be found experimentally. At the moment of 

 inception of the oscillations the amplitude will be infinitesimally small 

 and the tube resistances will generally be such that the initial value of 

 /xjS is considerably greater than unity. As the amplitude grows, the 

 plate resistance Ri tends to increase and the grid resistance to diminish 

 until at a certain amplitude the resistance ratio takes the value given 

 by equation (25). The oscillations then remain steady at this 

 amplitude. 



It may be noted that the amplitude relationship (29) holds so long 

 as the capacitances are maintained in the fixed ratio 



and is independent of their absolute values. If, therefore, the capaci- 

 tances are varied simultaneously while their ratio is maintained con- 

 stant, the oscillation frequency will be varied, but frequency stabiHty 

 will be maintained for all adjustments and the oscillation ampHtude 

 will remain constant. A similar result may be obtained by varying 

 the inductances simultaneously. 



It is instructive to examine the action of the added plate circuit 

 inductance in Fig. 4 in the light of the image parameters of the coupling 



