HT SUPPLIES 



Figure 37.3, which also provides a negative supply from the same trans- 

 former. The use of cold-cathode regulators will considerably reduce the 

 effect of mains voltage fluctuations on the output, but is not conspicuously 

 effective in reducing the output impedance, which will still be of the order of 



+300V 

 0-40 mA 



W 150/30 

 1//? 150/30 



1,250A 

 5W 



350-0-350 V 

 14— I 80mA 



-300VO- 



-vvv^-'-^Tnmr^-i- 



0-40mA 1,250il 20H 

 5W 



Figure 37.3 



hundreds of ohms. It is not possible to be more precise than this because 

 individual tubes vary appreciably in their abihty to maintain a near-constant 

 potential difference over a wide range of current. Cold-cathode-diode- 

 stabilized power packs are therefore suitable for applications where the 

 load is rather constant, such as precision oscillators, differential amplifiers, 

 etc. 



3-7kft 



♦ 85V^ 

 7-5mA 



Mains 



Figure 37.4 



Even greater independence of mains voltage fluctuations may be had by 

 connecting stabilizer circuits in cascade, as for example in the arrangement 

 in Figure 37.4, devised by Luke^ for supplying E.E.G. amplifiers. 



Electronically stabilized HT supplies 



In order to secure both independence of the mains voltage and a really 

 low output impedance it is necessary to use electronic stabilization, employ- 

 ing hard valves. Innumerable designs for doing this have been produced, 



587 



