EHT SUPPLIES 



The design of RF EHT transformers has been discussed by Barron^^ 

 Alternatively a range of ready-made coils are available from a number of 

 firms specializing in EHT generation equipment. 



Stabilization of EHT is particularly easy to accomplish using the RF 

 method. Lowe^^ describes a circuit for supplying Geiger-Muller tubes 



/mnrrv 





001JJ.F 



+350 v' 

 AOmA 



22K 



Figure 37.23 



which has a change of output voltage of less than 0-1 per cent for a 10 per 

 cent change in the HT voltage supplying the oscillator, or for a variation in 

 output current from zero to 32 ^A (full load). The scheme is shown in 

 outline in Figure 37.24. A fixed fraction of the output voltage is taken by 

 i?i and /?2 ^rid applied to the direct-coupled amplifier valve V^. Since the 



+ 315 V Unstabilized 



1600 V -C 

 EHT < 



tAA/Y^Jr^ 



T T H 



Control voltage 



-105V Stabilized 



Figure 37.24 



— 105 V fine is stabilized, V^ grid potential has a definite value when the EHT 

 voltage is correct. Departures of the EHT from the desired value are ampli- 

 fied in Fi and transferred via R^ to the suppressor of the RF oscillator valve 

 F2 in such a sense as to correct the departure. The oscillator and rectifier 

 circuits are closely related to Dickinson's in Figure 37.23, except that Lowe 

 uses Figure 37.21a type rectification and heats his rectifier cathode from a 

 separate RF oscillator, not shown here. 



599 



