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[AMPS] Distortion, amp design, and 813s (newbie alert!!)

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Subject: [AMPS] Distortion, amp design, and 813s (newbie alert!!)
From: (Tom Rauch)
Date: Wed, 19 Sep 2001 20:30:45 -0400
> almost zero dollars invested in them. I've been
> looking through some of Mr Orr's earlier books and
> there are several examples of class B linears for SSB
> use but I'm wondering how these would fare by todays
> standards?  How 'bad' would they be?  Even in a
> push-pull circuit?  With NFB ???

I can't comment about the expected IMD of 813's, but I can about 
push-pull operation and NFB.

In RF PA's, push pull is meaningless for distortion and IMD. 
Absolutely totally meaningless. It is a common misinformed myth 
circulating around that push-pull RF PA's have less on-band 
splatter or "better audio".

You might as well use parallel, so far as IMD or the "sound" is 

The only reliable and stable way to add negative feedback in an 
amplifier with adjustable tank circuits is to use a resistor that is 
NOT bypassed at the cathode of each tube, in series with the RF 
path to ground.

Stability might be an issue with four tubes.  

Use the lowest value near-zero inductance grid resistor you can 
right at each tube for swamping.
73, Tom W8JI 

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