EQUIVALENT CIRCUITS OF NETWORKS 



613 



is also the case for the effective transadmittance ^12 + i32i as well as for the 

 effective transimpedance Zu + Z21 . On the other hand, the quantity 

 Z I y 



— — , which appears in the network of Fig. 15 and which represents 



Zn 



the driving force per unit input voltage, is invariant (except for reversal in 

 phase) only for grounded grid and grounded cathode operation. Several 



(a) 



y2i 



yiiy22 



(b) 



(c) 



k = 



y2t 



y22 + yii 



V2 



Va 



Fig. 20 (a, b, c) — Three forms of equivalent circuits of the grounded grid triode valid 

 at all frequencies. 



admittance and impedance relations may also be pointed out. For example, 

 the input short-circuit driving-point admittance jSn is equal for grounded 

 cathode and grounded plate operation and the same is true for the output 

 short-circuit driving-point admittances ^22 for grounded cathode and 

 grounded grid operation. Moreover, it is also seen that the input short- 

 circuit driving-point admittance ^n for grounded grid operation is equal to 

 the output driving-point admittance 1822 for grounded plate operation. A 



