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

To: "Steve Thompson" <>, <>
Subject: Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback
From: "Tom Cathey" <>
Date: Thu, 22 Dec 2005 12:35:33 -0500
List-post: <>
Very interesting comments.

It certainly IS an eye opener when you see what each driver plate 
dissipation needs to be for an all class A chain. But an easy way to 
maintain high IMD figures.

I'm considering doing just that for 40-10M. ... using either a string of 
class A tetrodes  or class A GG hi mu triodes.   But I worry about the grid 
driven tetrodes and stability. A bear to keep stable above 40M.

Would there be a major disadvantage to running the whole tetrode chain in GG 
with standard voltages on the grid and screen?  It seems it would be much 
easier to tame and also have GG neg feedback and pass thru power to the 
output.  Maybe link coupling between stages work work.

Tom, K1JJ

Tom, K1JJ

> Very! It's a whole new world where driver stages are much bigger than
> you think they need to be. Say your output stage will deliver the wanted
> power at -50dBc IMD3 - if the driver also runs at -50, the overall
> result will be -44dBc. The driver has to run at -56 or better to affect
> the overall IMD by 1dB or less. You churn the linearity numbers, and
> it's a bigger device than you might think at first. With older
> semiconductors where each stage has a gain of 8-10dB, a typical lineup
> would have 1 driving 2 driving 4 identical devices, all running the same
> class A dissipation - massive overkill by class AB standards (imagine
> 4CX250 driving 3-500 driving 2x3-500).
> Steve
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