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BELL SYSTEM TECHNICAL JOURNAL 



These values are not very critical, however, since when we put R 

 = Rq and Ec = — Eb/lix the power drops by about ten per cent. 

 The last condition is that for maximum power at maximum gain, 



-ZO -18 -16 -14 -IZ -10 -6 -6 -4 -2 



VOLTS GRID POTENTIAL 



Fig. 10 — Maximum power output as a function of the grid potential. EL tube No. 

 109,150. Ep = 120, E = Ec, R = Ro 



in which the output power for a definite alternating grid potential 

 is maximum. In view of the fact that it approximates optimum 

 conditions and is much more convenient as a basis for calculation, 

 we shall use the maximum power — maximum gain criterion of the 

 performance of tubes. 



Current and Power Relations. 

 The preceding analysis has shown that the maximum power 

 obtainable at maximum gain without drawing grid current and 

 without exceeding the negative end of the characteristic — at which 

 grid potential variation produces substantially no plate current 

 variation — is to be found at a grid voltage about midway between 

 the two voltages specified by these conditions. It is again instructive 

 to compare the predictions of the two theories as to the power dissi- 

 pated in the tube, the a.c. power delivered to the load, the second 

 order modulation, and the relations between these quantities at this 



