50 



BELL SYSTEM TECHNICAL JOURNAL 



2 2.25 



200 300 400 500 



PEAK EXCITING VOLTAGE 



Z 



UJ 



60 O 



40 O 



30,7 



Fig. 17 — Djmamic output and efficiency of a screen grid tube. Eh = 3000 volts, 

 Eo= - 100, Es = 400 volts. 



Conclusions 



It has been shown from both theory and experiment that there is a 

 marked difference between the dynamic output characteristics of Class 

 B and Class C amphfiers as defined, particularly in the lower portion 

 of the curves. This difference is the more pronounced the farther the 

 grid bias voltage is moved from the cut-off point. In general, Class C 

 operation is more efficient than Class B operation because the flow of 

 plate current is limited to a smaller portion of the cycle which includes 

 the portion in which the plate voltage is lowest. 



It must be borne in mind that in a radio telephone transmitter where 

 modulation is effected at low power level and the modulated carrier 

 amplified, the dynamic characteristic of the output current will be the 

 resultant of the dynamic characteristics of all of the intermediate 



