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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: Mon, 19 Dec 2005 12:32:08 -0500
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Hi Marv,

Gee, that feed forward correction method sounds like something that would be 
ideal for the FT-1000D. As you said, it could be later moved from rig to rig 

So far all I've seen on the web are ivory tower block diagrams, etc. Is 
there a tested circuit available somewhere to build up or a commercial 
surplus unit? Even something that has suggested chip choices with a circuit 
I could then modify to my use would help.

For this particular project, I don't mind building up the two stages to go 
from 5mW to 250mW using a chip and a tube, but this feed forward correction 
idea could open the door to setting up other clean linear systems from 
exisiting stand alone linears I have now in the shack..

Just to double check... it requires TWO inputs:  The 5mW, and  the 1000D 
200W module output for sampling, correct?   And the big linear final would 
have it's own negative feedback loop back to the tube driver, if used, 
independent of the feed forward system? [assuming we don't use your 200 ohm 
swamped system and still use a tube to drive the final]

Tom, K1JJ

Hi Tom,
   The FF system would be entirely external to your FT-1KD -- It just 
connects between the rig's output the outboard linear, plus an input from 
the low level tap.  Therefore, transportable to a new rig with a low level 
out -- an easy addition, if necessary.  It could even be left in line with 
only a slight (1-2%) loss of power when not in use.

   Regarding the link, which looks to be more of a mechanical diagram than a 
schematic, it might not be GG.  The final neutralization ckt. resembles a 
grid driven stage.  The 1st-2nd stage coupling also appears to be more 
suitable for grid driven operation.  Perhaps, it's 3 grid driven stages? 
Where have we seen that before...

73 & Good evening,
  Marv WC6W

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