POWER AMPLIFIER FOR MODULATED WAVES 



473 



characteristic shows the curvature that would he obtained if rul)e 2 

 were not allowed to come into action. With proper adjustment of the 

 bias and relative excitation on Tube 2 this effect is eliminated and the 

 characteristic continues to rise up to the desired peak amplitude. 



200 



< 150 



70 5 



20 o 



10 20 30 40 50 60 70 80 90 100 110 120 130 140 



RMS INPUT POTENTIAL IN VOLTS 



Fig. 3 — Dynamic characteristics of an experimental low-power 

 high-efficiency amplifier. 



The radio-frequency plate voltage of Tube 1 is seen to be twice 

 that of Tube 2 up to the point where curvature begins, and then to 

 increase only slightly between the carrier output and peak output. 

 The plate current of Tube 2 commences just before the carrier point 

 is reached and rises twice as rapidly as the plate current of Tube 1. 

 The equality of plate currents and radio-frequency plate potentials 

 on the two tubes at the peak of modulation indicates that the tubes 

 are contributing about equally to the instantaneous output at this 

 point. 



The high radio-frequency plate potential of Tube 1 at the carrier 

 amplitude results in an efficiency of 63 per cent, and by integrating the 



