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BELL SYSTEM TECHNICAL JOURNAL 



with a i)re(i()iniiiam second haniionic. At a point slightly above 

 .047 watt one or more of the grids becomes positive to the filament 

 for part of a cycle and draws current. On account of the high im- 

 pedance of tlie circuits supplying the grids this immediately results 

 in a flattening of the top of the wave which is well developed at .075 

 watt output. This flattening of the top of the wave compensates to 

 some extent for the curvature of the lower part of the tube character- 



> 



2.15 WATTS 

 Input Voltage — 



3.40 WATTS 



680 WATTS 



Fig. 13 — Amplifier No. 2; ],()()U c.p.s., load .SOO ohm resistance 



istic so that the curve becomes more symmetrical with regard to the 

 zero axis although more distorted. This corresponds to the fall of 

 the second harmonic and increase of the third. At an output of .140 

 watt this compensation is more nearly complete than at any other 

 output. At still higher outputs the top of the wave is still more 

 flattened and the plate current is reduced to zero for a considerable 

 part of the cycle so that the output wave becomes nearly rectangular 

 as shown. This corresponds to large amounts of all harmonics. 



