[Amps] Class F PA circuit tricks to improve efficiency

[John Lyles]

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 at jeremy.mv.com>
> Subject: Re: [Amps] gg feedthru power
> To: <jtml at vla.com>, <amps at 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