POWER PACKS 



SO successful at supplying, say, a double-channel stimulator; the sort of 

 distressing effect one would find would be that turning up the amplitude 

 control of output number 1 produces the expected effect, but also slightly 

 reduces the amplitude of output number 2. This results from a reduction 



J 



O O 



Neutral Phase 



Figure 37.1 



Mains Input 



in HT voltage caused by the higher current drain of the No. 1 channel, and 

 would be mitigated if the power pack regulation were better, i.e. if the HT 

 were stabilized. It is possible to use stimulators fed from unstabilized 

 supplies, but not very convenient; none of the controls can be properly 



Neutral Phase 



Figure 37.2 



Mains input 



calibrated. If financial stringency dictates the use of simple power packs 

 in instrument applications, then the output impedance should be kept as 

 low as possible by using a low resistance choke, and rectifiers rated for a 

 rather higher current than necessary. The extremely low forward resistance 

 of germanium and silicon junction rectifiers would also be a help here, but 

 as yet they are not very cheap. 



Cold-cathode-diode-stabilized HT supplies 



The design of cold-cathode-diode circuits has been discussed in Part I 

 and a complete HT supply stabilized in this manner has the appearance of 



586 



