198 



BELL SYSTEM TECHNICAL JOURNAL 



The values of R'g and C'g given in Table IV' were calculated on the 

 assumption of a pure resistance load R in the plate circuit. If the load 

 in the plate circuit is an impedance Z = R-\-j x, it will be foimd that 

 the sign of the apparent shunt resistance R'g will depend upon the 



Fig. 12 — Tolul .Xmplification of Transformer Coupled Receiver and Effect of "Feed 

 Back" on Loop Resistance 



sign of the reactance .r. For a capacitive load, the resistance R' i 

 will always be positive, but for an inductive load, R'g may in some 

 cases become negative and we then have "feed back" or regeneration 

 occurring through the tube. The negative resistance introduced in 

 the circuit belf)w the resonance frequency may in certain cases be 

 so high that it more than neutralizes the positive resistance of this 

 circuit which means that the set will start to oscillate or "sing." 



