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Re: [Amps] 4CX1500 class AB1 vs. AB2

To: Tom W8JI <w8ji@w8ji.com>, Gary Schafer <garyschafer@comcast.net>,'Ian White GM3SEK' <gm3sek@ifwtech.co.uk>, amps@contesting.com
Subject: Re: [Amps] 4CX1500 class AB1 vs. AB2
From: Peter Chadwick <g3rzp@g3rzp.wanadoo.co.uk>
Reply-to: g3rzp@g3rzp.wanadoo.co.uk
Date: Thu, 2 Nov 2006 23:26:31 +0100 (CET)
List-post: <mailto:amps@contesting.com>
Tom said:
>As a matter of fact, I'd never consider it a good idea.<
That makes two of us then, Tom.
Putting NFB on in a grounded cathode amp isn't that difficult - some resistance 
in the cathode - say 10 ohms - with a suitable RFC across it so the effective 
bias doesn't vary has a very useful effect. I got about 12dB improvement in 3rd 
order products from that in my AB2 pair of 4-250As. But I do use a shunt 
regulated bias supply and a regulated screen supply, as well as about 200 ohms 
of grid shunt resistance for the RF load - my driver is an FT102, so the SWR 
doesn't worry it.
73
Peter G3RZP
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