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BELL SYSTEM TECHNICAL JOURNAL 



frequency of operation, or that the time constant of Co and Ro is large 

 compared to the time of one cycle of the operating frequency. In this 

 event, then, the voltage across Co will remain constant at E,, during a 

 complete cycle. Let it also be assumed that the choke coil Lh is of 

 sufficient inductance that the current /& is maintained constant 

 throughout the cycle. 



lb 



Lb 



Eb 



3 



lb 



Fig. 1 — -Schematic of amplifier plate circuit with resistance load. 



Then by applying Kirchoff's laws to the circuit. Fig. 1, remembering 

 the assumptions regarding Co and Lb, we find the following relations 

 must hold at any instant: 



or 



and 



also 



Eb = ipRp + ioRo 



Cp = Eb — ioRo 



id = ip — /ft, 



lb = Average of ip over 1 cycle, 



(1) 



(2) 

 (3) 

 (4) 



since the average current through Co must be zero.* 



Then let it be assumed that the grid of the tube is excited and biased 

 in such a manner that the plate current, ip, will vary sinusoidally as 

 illustrated in Fig. 2. When the resistance Rp is at its minimum value, 

 ip will be a maximum and will be the sum of lb and io, [(1) and (3)]. 

 Also ep will be a minimum, (2) ; see point 1, Fig. 2. As Rp is increased 

 by the grid potential going in the negative direction, ip will be reduced 



* See Table of Symbols at end of this paper. 



