[Amps] Filtering capacitor in a HV PS: How low can you get awaywith?

[Ian White, G3SEK]

Angel Vilaseca wrote:
>
>I am building a 2500 V power supply for a one-KW transmitter. It will 
>use 2 4CX20Bs.
>
>I have two oil-filled capacitors: 2.5 KV 40 uF  and a 4 KV 25 uF.
>
>I feel quite uncomfortable using the 40 uF 2.5 Kv one, because it would 
>work very close to its voltage limit.
>
>On the other hand, the 4 KV 25 uF would be OK as far as voltage is 
>concerned, but would not 25 uF be too low?
>
I'd agree with Steve - use the 25uF, since this is a low-current supply 
by most people's standards on this list.

>Is there a rule of thumb ?  How low can you get away with capacitance 
>in a HV power supply feeding two tetrodes?
>
The really isn't a rule of thumb - it's more a question of: how many 
percent of 100Hz AM are you prepared to tolerate?

If you really, really want to know how the 25uF capacitor will perform, 
then download Duncan Munro's "PSU Designer" software (go via my 'In 
Practice' page, URL below, and also pick up the data file that supports 
HV rectifiers).


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek/in-prac