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

[R.Measures <r@somis.org>]

On Jul 17, 2004, at 10:16 AM, Ian White, G3SEK wrote:

> 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.
> >
> > Ã  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.
**  No more so than any other tetrode.

> 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'.

**  Not all zeners have the sameËâ Z.
> (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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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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