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[Amps] Class F PA circuit tricks to improve efficiency

To: amps@contesting.com, km1h@jeremy.mv.com
Subject: [Amps] Class F PA circuit tricks to improve efficiency
From: "John Lyles" <jtml@losalamos.com>
Reply-to: jtml@vla.com
Date: Wed, 31 Mar 2010 14:46:00 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
This time i added a subject line, sorry. 

Carl, I didn't build the Tyler output modification, as the tube manufacturer in 
France doesn't recommend 'efficiency improvements' via plate current waveform 
modification. Although i did notice a copper slug
in their own test cavity amplifier that was said to help minimize second 
harmonic power in the output. I am sticking to class AB2 - to B. I was 
referring to the effects on plate current waveshape (and measured
DC to RF conversion efficiency) that MIGHT happen if a quarter wave stub was 
placed at the wrong place, distance from the plate to the stub. However, it 
would effect even harmonics and not odd ones, so it might
have zero net effect. I hoped to hear someone's experimental evidence of this 
before I make big mechanical design changes.

In some of the medium wave b'dcast transmitters with tubes, though, I've seen 
that circuit in use. The Collins 5 kW power rock did it. RCA had a nice app 
note on it, Power Tube Engineering Note IEN-4. They
talked about the 5762/7C24 being overdriven with flat topped grid voltage in 
the BTA5U, and having third harmonic parallel resonant traps in the cathode and 
the plate leads to the tube.  
Its tricky to try and design these same equivalent resonators into a coaxial 
line circuit (a cavity). I can scan and email the app note, dated 1964.

John
K5PRO

> Date: Wed, 31 Mar 2010 09:40:32 -0400
> From: "Carl" <km1h@jeremy.mv.com>
> Subject: Re: [Amps] gg feedthru power
> To: <jtml@vla.com>, <amps@contesting.com>

> Thats how I remember it also John but its been a long while since I read it!
>
> BTW, when you mentioned the Tyler circuit in that 500KW amp what efficiency
> improvement were you getting?  What class and how is it driven?
>
> Carl
> KM1H
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