DOUBLE-SIDED AMPLIFIERS 



spaced, so the output is not a perfect copy of the input; the problem is more 

 serious with high level and power amplifiers, where the grid is swung over a 

 wide range of voltage. In particular, triode characteristic curves tend to 



Figure 12.5 



Figure 12.6 



bunch in the bottom right-hand corner of the working region {Figure 12.7) 

 and pentode curves at the bottom right and top left {Figure 12.8). The effect 

 of this is that if the valve be fed with a sine wave input, the triode output 



Figure 12.7 



Figure 12.8 



tends to be 'squashed' on the positive peaks and the pentode output to be 

 squashed on both positive and negative peaks {Figures 12.9 and 12.10). A 

 waveform of the Figure 12.9 type is produced by adding to a pure sine wave a 



Figure 12.9 



Figure 12.10 



small proportion of its even harmonics, notably the second {Figure 12.11). 

 Similarly, a waveform of the Figure 12.10 type is produced by adding to a 

 pure sine wave a small proportion of its odd harmonics, notably the third 



178 



