88 BELL SYSTEM TECHNICAL JOURNAL 



and the other a variable capacity "ganged" together with C3 and 

 equal to 



(1 + k') 



Cs 



(1 - P) 



In order to insure fulfillment of the requirements of this theory, it 

 was mentioned above that the oscillator should be relatively free from 

 harmonics, so that fp and r^ may be taken as pure resistances. That 

 this requirement can be successfully met may be demonstrated by 

 reference to Fig. 15 and consideration of the means which would be 

 employed if the circuit represented an amplifier with e„ impressed on 

 the grid of a following tube instead of on the grid of the driving tube 

 itself. In such an arrangement, it is well known that the distortion is 

 least when the impedance looking out of the plate of the driving tube 

 is made materially larger than the internal plate resistance of the tube 

 itself; and, second, when the impedance looking back out of the grid 

 of the driven tube is made materially smaller than the internal grid 

 resistance of the tube itself. The conditions which determine how 

 nearly these two requirements may be met in the oscillator tube are 

 governed by (22). Thus 



This should be small in order that the first requirement mentioned 

 above should be fulfilled. Hence fxkyJLo/Li should exceed unity by 

 as little as is consistent with reliable oscillation. \\'hen we come to 

 consider the second of the requirements for decreasing harmonics we 

 obtain an expression analogous to (34), namely: 



so that the requirement that the impedance looking back out of the 

 grid should be less than the grid resistance is satisfied by the same con- 

 dition as that required by (34) ; namely, that fxk^lL^/Li should exceed 

 unity by as little as is consistent with reliable oscillation. 



From Fig. 17, by regarding C3 and G as zero, the feed-back type of 

 oscillator is obtained. Again, when G and d are zero, the Hartley 

 oscillator results. The stabilization both of the feed-back oscillator 

 and the Hartley type by the method shown on the figure was not 

 described in the analysis of Figs. 3 and 9 inasmuch as the present 

 method places the stabilizing element directly in the tuned circuit, 

 whereas the former method placed it between the tuned circuit and 

 the vacuum tube. 



