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

To: Tom Cathey <>
Subject: Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback
From: Gary Schafer <>
Date: Sat, 17 Dec 2005 12:01:25 -0500
List-post: <>
As a follow up to specing IM products to PEP.
Some of the same tricks are used by manufacturers when specing 3rd order 
intercept points for VHF/UHF pre amps. Some will spec them with 
reference to the input levels required to reach the intercept point and 
some will spec them to the output level of the pre amp when the 
intercept point is reached. So if the pre amp has say 15 db of gain, 
then it looks like the intercept point is 15 db higher than the same amp 
speced to input levels. You have to read the fine print. Sometimes they 
don't even supply the fine print.

Gary  K4FMX

Tom Cathey wrote:
> Marv,
> 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 
> point.
> 73,
> Tom, K1JJ
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