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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: Thu, 15 Dec 2005 14:20:28 -0500
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I like BOTH suggestions, Gary!

Having the input link phase reversable opens the door for GG driving GG 

For the GG  input drive NFB resistor, what value would you try for an 8877 
input?  It appears to need to handle some input power too. How about a 
bypass cap across the resistor, or wud you leave it unbypassed?

I am also going to try Frank/GFZ's idea of sampling some RF from the GG 
final's plate with a pick up plate and feeding it back via turns over the 
filament choke. This is a directly heated cathode amp. He added that maybe 
the cold end of the winding can have a variable cap or inductor to ground - 
to adjust phase, if need be. Not sure how that will work multiband, but will 
give it a try anyway.

I'm open to ideas to try.

Tom, K1JJ

> Hi Tom,
> Put the resistor in series with the input coupling capacitor.
> If you want to experiment with negative feedback with multiple GG drivers 
> you might try link coupling between stages. You can reverse the link at 
> the feedback point to get the out of phase signal. You will need at least 
> a 2 stage amp to do this. Maybe an 811A in GG as a driver for the 4-1000.
> Put a small coil at the bottom of the input link of the 811A to lift it 
> slightly above ground. Couple the plate of the 4-1000 to that point 
> through a small capacitor.
> 73
> Gary  K4FMX

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