LOAD CARRY I XG CAPACITY OF AMPLIFIERS 



589 



the other hand tlie gain-load curve does not show any appreciable 

 decrease of gain until the amplifier is considerably overloaded. 



For high power amplifiers and those amplifiers in which it is desired 

 to reduce distortion to a minimum the push-pull arrangement of 

 tubes has been used because with this arrangement the even har- 

 monics generated in the tubes are suppressed in the output circuit. 

 That the suppression is quite effective is shown by the curves and 



Input Voltage 



Fig. 16 — Amplifier No. 4; 200 c.p.s. input; load 7,000 ohm negative reactance 



oscillograms of Figs. 8, 9, 13 and 14 which were taken on the No. 2 

 and No. 3 amplifiers. These show that the even harmonics are 

 very small at all loads and that the third harmonic increases suddenly 

 at a point which in view of the plate and grid biasing potentials em- 

 ployed may be taken as the point at which grid modulation commences. 

 On the oscillograms this point is not so clearly marked as in the 

 previous cases but on those for No. 2 there is a slight flattening of 

 the ends of the curve which is noticeable at 1.7 watts but not at 

 1.36 watts. On No. 3 amplifier where the impedance of the circuit 



