LOAD CARRYING CAPACITY OF AMPLIFIERS 



581 



stanlialK' the case may be seen by inspection of the figures. In the 

 first oscillogram of Fig. 11 there is shown the characteristic for 

 amplifier No. 1 under 130 volts plate supply and .047 watts output 

 where the amplitude of grid voltage is such that no grid becomes 

 positive with respect to the filament nor is the plate current reduced 

 to zero at any part of the cycle. Under these conditions the tube 

 characteristic as shown in the oscillogram has the same nearly para- 

 bolic shape as is found l)y other methods. The analysis made at 



Fig. 6 — Amplifier Xo. 1 — Plate voltage 130-V, 1,000 c.p.s. input, 

 and distortion with output 



Variation of gain 



this point showed 7.3% second harmonic, .8% third and less than 

 .1% fourth and fifth harmonics. The mathematical analysis of the 

 problem expresses the Ec — h characteristic of the tube by a power 

 series and shows that the coefficient of the second power term in the 

 series is the principal factor in producing second harmonic. The 

 percentages of harmonic given therefore are such as would be ob- 

 tained from a tube having a nearly parabolic characteristic. 



Analyses made at lower outputs showed that the amount of second 

 harmonic present varies with the power output in a manner de- 

 scribed by a slightly curved line on the logarithmic scale used (Fig. 6). 

 The third and higher harmonics are negligible at low outputs but at 



