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BELL SYSTEM TECHNICAL JOURNAL 



active grid loss which as already mentioned comes about because of the 

 appreciable electron transit time. Fig. 8 gives a plot of the push-pull 

 input shunting resistance of this tube as a function of frequency. The 



80 



70 



60 



50 



40? 



I- 

 Z 

 UJ 



a. 



30 § 



o 



20 



10 



100 



90 



80 70 60 50 40 30 20 



CONTROL GRID POTENTIAL IN VOLTS 



10 



Fig. 6 — Mutual characteristics of the double pentode tube. 



40 



30 



20 



10 



value of 30,000 ohms at 150 megacycles is to be compared with 2000 

 ohms, a typical value for two conventional tubes in push-pull. At 300 

 megacycles the input resistance of the twin pentode is still above 5000 

 ohms while for conventional tubes it is so low as to make them com- 



