66 



BELL SYSTEM TECHNICAL JOURNAL 



grid potential is — 15 volts. Under these conditions, the average 

 characteristics are: Ip = 42 ma, A = 5 ma, ii = 156, Rp = 52,000 

 ohms, and Sm = 3000 micromhos. 



Curves showing the amplification factor, n, the plate resistance, Rp, 

 and the transconductance, Sm, for several different values of grid bias, 

 are shown in Fig. 10. They correspond in general form to those 



200 

 160 

 120 

 80 

 40 

 



120 000 

 100 000 

 80 000 

 60 000 

 40 000 

 20 000 

 



■ ^«_5_ 



4 



3~ 

 2 



5000 



Z ^ 4000 



^§ 



D 5 3000 



Q O 



Z g 



8 5 2000 



<cl 



I- 



1000 



2 



3_ 



4_ 



s" 



200 



300 400 

 PLATE VOLTS, Ep 



500 



600 



700 



Fig. 10 — Amplification factor, plate resistance, and transconductance of a power 

 pentode as functions of the plate voltage, with various values of control-grid voltage 

 as parameters. Screen voltage, E„ is maintained constant at 250 volts. 



shown in Figs. 3 and 5 for the screen-grid tube. The maxima in some 

 of the plate-resistance curves result from the fact that the corre- 



