THEORY OF MULTI-ELECTRODE VACUUM TUBE CIRCUITS 667 



admittances. The impressed variable electromotive forces are tp and 

 eg in series with the impedances Zp and Zg, respectively. We will 

 designate by Ep and Ip the total plate voltage and current, respectively, 

 while the corresponding quantities for the grid are Eg and Ig. In the 



Fig. 1 — Three-electrode vacuum tube and circuit. 



absence of the variable electromotive forces the d-c. values of these 

 voltages and currents are Epo, Ipo, Ego, and Igo, respectively, while the 

 increments due to the impressed forces are ep, ip, Cg, and ig, respectively. 

 Similarly, g and p denote the incremental voltages across Zg and Zp. 

 All quantities referring to currents and voltages are instantaneous 

 values. 



We will now assume that Ip and Ig are functions of Ep and Eg, 

 and that we can derive from these functions the expansions 



where 



Omn 



Ip 7 . Omn"n Cg , 



1 6('«+")/„ 



^0 2^P'nnep €g , 



1 a (""+")/„ 



mini dEp"'dEg'' ' 



Pmn 



mini dE^^'dEa" 



(1) 



(2) 



evaluated at the operating point (Epo, Ego). 



The important tube parameters are by definition 



(3) 



where r denotes electrode resistances, /x the mu-f actors, and 5 the 

 transconductances. 



