THEORY OF MULTI- ELECTRODE VACUUM TUBES 



67 



spending plate-current curves turn up at the higher plate potentials 

 and thus have points of inflection. 



In Fig. 11, the plate current is shown as a function of control-grid 



-20 -15 -10 



CONTROL GRID VOLTS, Eg 



Fig. 11 — Plate current-grid voltage characteristics of a power pentode, with dynamic 

 characteristics for resistance loads of 6000, 10,000, and 20,000 ohms. 



voltage for various values of the plate voltage, with the screen potential 

 constant at 250 volts. The curves are very similar to corresponding 

 ones for the screen-grid tube shown in Fig. 4. Here, curves are 

 included at such low plate voltages that a large falling off in plate 

 current occurs. 



In Fig. 12, the output power in watts, and the second and third 

 harmonics, expressed in decibels below the fundamental, are shown as 

 functions of peak volts for a sinusoidal input applied to the grid. 

 These data were obtained under the normal operating conditions 

 previously given, and with the indicated load resistances. Since the 

 curves are typical in form of those obtained in several types of multi- 

 electrode tubes, it will be of interest to examine them in some detail. 



