10 



DIFFICULTIES WITH SINGLE-SIDED AMPLIFIERS 



Amplifiers which consist of a simple string of cascaded stages like the 3 

 stage a.c. coupled amplifier in Figure 10.1 and the 3 stage direct coupled 

 version in Figure 10.2 are called single-sided, for a reason which is apparent 



Input 



Figure 10.1 



Input 



Figure 10.2 



later. In operation they present certain difficulties, some of them insur- 

 mountable, which render them unsuitable for biological work. 



MOTOR BOATING 



It is desirable and economical if all the HT power for an amplifier can be 

 supplied from a common source, either battery or 'power pack'. An attempt 

 has been made to do this in Figures 10.1 and 10.2, where a common HT 

 battery is shown. It is highly unlikely that these circuits would work — pro- 

 bably they would oscillate violently, no matter what the input signal did. 

 The following give the reasons why. 



159 



