122 



BELL SYSTEM TECHNICAL JOURNAL 



•frequency shift, large as it is, is much less than the shift observed in 

 tubes of poorer design and correspondingly lower efficiency. 



The dependence of the output and efficiency as well as frequency 

 upon the grid current is shown in Fig. 23. These data were taken with 



^ 4.0 



5 



540 zl 



> a. 



Z Q. 



100 120 140 



160 180 200 220 240 260 280 300 320 340 

 GRID CURRENT IN MILLIAMPERES 



Fig. 23 — Result of variation of grid current, other adjustments fixed, on tube of 

 Fig. 19. / = 532 megacycles. 



a grid potential of 450 volts and a fixed circuit adjustment correspond- 

 ing roughly to a frequency of 532 megacycles. The current to the 

 grid was varied by adjusting the temperature of the filament. The 

 maxima observed in both the output and the efficiency correspond to 

 conditions for which the grid current is limited primarily by the 

 available emission rather than by space charge. As conditions corre- 

 sponding to complete space charge are approached the output and 

 efficiency fall off rapidly. The limit on the permissible grid dissipa- 

 tion prevents the extension of these curves to the condition of complete 

 space charge. Because of this dependence of output on grid current, 

 the adjustment of filament temperature is e.xtremely critical. 



