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Re: [Amps] Historical question-probably OT

To: g3rzp@g3rzp.wanadoo.co.uk
Subject: Re: [Amps] Historical question-probably OT
From: R L Measures <r@somis.org>
Date: Sat, 27 May 2006 03:20:45 -0700
List-post: <mailto:amps@contesting.com>
On May 26, 2006, at 11:45 AM, Peter Chadwick wrote:

> At Dayton, I got a 1960 ARRL Handbook ( got to update the station!)  
> for my collection. It has an interesting HF amplifier in it, using  
> a pair of 4X250, (NOT 4CX) running, it is claimed AB2 passive grid,  
> although the drive level discussed seems to me too low for AB2. It  
> is enough for AB1, though.  Some other interesting historical  
> features are the power supply, which used germanium rectifiers. A  
> transformer with two 325 volt windings, each voltage doubled and  
> wired in series, and no bias regulation, which again makes me query  
> the AB2. Also, a fixed link coupled output network, pretty well  
> necessitating a tuner - shades of today's solid state stuff!
> Another point of interest is the modification of the tube sockets  
> to reduce the back pressure so that a big axial fan can be used for  
> tuning. The design was published in a 1958 QST. Has anyone here  
> ever heard of any of the 250 series being run for linear amp  
> service in AB2? I've only ever seen AB1 discussed.
> 73

Since 4cx250Bs and their cousins do not have a striped cathode and  
aligned grids like the 4cx1500B and 4cx600J, they are not anywhere  
close to linear in grid-driven service whenever grid current flows.
   Without RF-NFB, such as is the case in G-G / cathode-driven, AB2  
makes some serious amounts of doo-doo.

> Peter G3RZP/W6 (this week)
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>

R L MEASURES, AG6K. 805-386-3734
r@somis.org



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