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Re: [Amps] Schematics  for 4CX250B GG HF amplifier

To: g8on@fsmail.net, JeanPierre.Behiels@electrabel.com, amps@contesting.com
Subject: Re: [Amps] Schematics  for 4CX250B GG HF amplifier
From: Colin Lamb <k7fm@teleport.com>
Reply-to: Colin Lamb <k7fm@teleport.com>
Date: Wed, 15 Aug 2012 10:43:43 -0700 (GMT-07:00)
List-post: <amps@contesting.com">mailto:amps@contesting.com>
While Peter's reference to the Eimac article is excellent, I just want to 
report that there has been some reports by users that it might be possible to 
use the 4CX250 series of tubes in a ground-grid arrangement without a screen 
voltage.  The control grid on this tube is extremely sensitive and easily 
destroyed, so the "normal" grounded grid connections will destroy it.  A few 
ham have experimented with grounding the screen grid and connecting the control 
grid either to the cathode or through a large resistor to the screen.  

I only mention this because hams are experimenters.  I have seen such circuits 
and claims that they work, but no hard documentation.  I would not use a tube 
in such a circuit unless I was prepared to test and monitor the actual power 
dissipated by the grids to verify they are within limits - and that the total 
operation is desireable.  

Over the years, I have seen at least two articles on using the tube in this 
manner.  I am not recommending this circuit nor vouching for it.  Similar 
arrangments, with other tubes, are used in modulators and audio amplifiers - 
but just because a circuit appears in print does not mean it is good.

73,  Colin  K7FM
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