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

To: "Ian White, G3SEK" <>
Subject: Re: [BULK] - [Amps] HF and 4cx250b's
From: R.Measures <>
Date: Sat, 17 Jul 2004 21:26:04 -0700
List-post: <>

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

à 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.
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.

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) _______________________________________________ Amps mailing list

Richard L. Measures, AG6K, 805.386.3734.

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