Re: [BULK] - [Amps] HF and 4cx250b's

["Ian White, G3SEK" <G3SEK@ifwtech.co.uk>]

R. Measures wrote:
> On Jul 15, 2004, at 7:23 AM, Steve Katz wrote:
>
> > 4CX250Bs require a regulated screen supply, making the PSU design more
> > complex.
>
> ð  However, the screen current is so low in a 4cx250B that it often 
> goes negative, so the tube  is ideally suited for using a simple 
> zener-string shunt screen regulator connected to the LV end of the HV 
> bleeder-R.
> http://www.somis.org/D-a-10.GIF
> This circuit happily protects the tube from any possible failure mode.

BUT - the 4CX250B is very sensitive to variations in the screen voltage.

See http://www.ifwtech.co.uk/g3sek/cleansig/imd1.htm
for results of GW4FRX's practical measurements of IMD with different 
kinds of screen supply. A zener supply was notably worse than a true 
stabilized supply, especially for the higher-order products that make 
your signal 'wide'.

(Disclaimer: Yes, I do sell stabilized screen supplies commercially... 
but that's because I believe they make a difference.)


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