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Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback

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Subject: Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback
From: "Tom Cathey" <>
Date: Sat, 17 Dec 2005 11:45:35 -0500
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Just as a note on your Hughes sample amplifier URL below....

I see no negative DC bias on either the 4CX-250 nor the 4X10. Strange that 
it's not there. Bias is OK on the 6146. Would appropriate bias be introduced 
via an RF choke at the grid of each tube?  Should the 4CX-350 run deep class 
A like the 6146?  Also, the schematic shows the 4X10 with a grounded 
cathode, though it uses a directly heated filament. Would you bypass the 
filaments with .01's for the equivalent circuit and still have the 
feedback/neutralization work OK?  Just want to double check...

I'm trying to scale this down for a 4CX-3000 with the same driver chain.

As a note to Bill.....   The 6db manufacturers peak IMD test is very 
interesting. I see it used all the time in literature...  :-0   I never 
realized what they were doing.
Much like the old F-B antenna specs.

Yes, I will put together a two tone set up and get some real numbers, though 
I am convinced that the FT-1000D 10mW tap is going to be usable at this 

Tom, K1JJ

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