46 



BELL SYSTEM TECLINICAL JOURNAL 



at cut-off. The relative effect for other biases is practically the same 

 as for the case shown. 



Fig. 15 shows the dynamic output currents and efficiencies for a 



4.25 



3.25 

 3.00 

 2.75 

 2.50 



0. 1.75 



0.75 



0.50 



0.25 







50 ^. 



30 uj 



200 300 400 500 



PEAK EXCITING VOLTAGE 



Fie IS^Dynamic output and efficiency of a tliree-element tube. £fc = 3000 volts, 



ix= 10, Zo = 1500 ohms. 



screen grid tube which is identical in construction with the three- 

 element tube except for the addition of the screen between the grid 

 and plate. The \j. of this tube considering the screen to be the plate 

 is about 4, so that the cut-off bias is about - EJ\. The curves of 



