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

[R.Measures]

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.
>>
>> 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.
>
**  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 same˙∆ 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