[AMRadio] origin of Class B

John Lyles jtml at losalamos.com
Thu Feb 16 17:00:33 EST 2006

Loy Barton of RCA wrote one of the first class B high power audio amplifier reports. He developed the concept of plate modulation with a high level push pull audio driver for his thesis at Univ of Arkansas radio station. You can read the report from 1930 here:


I summarized the events which led to Barton's paper in QST in 1931, followed by Art Collins paper in 1935 on the benefits of this approach.



> Message: 4
> Date: Wed, 15 Feb 2006 18:48:52 -0500
> From: "Mike Sawyer" <w3slk at uplink.net>
> Subject: Re: [AMRadio] AM Transmitter Advice??
> To: "Discussion of AM Radio" <amradio at mailman.qth.net>
> Don, K4KYV said: Sometime in the late 1920's, it occurred to someone that 
> class-B linear
> amplification would work just as well for audio as for rf, and the class-B
> audio amplifier was developed.  The unusual thing about this setup was the
> large audio transformer required.  Many rf linears were single-ended, and
> depended on the fiywheel effect of the rf tank circuit to supply the missing
> half of the sinewave output.  With class-B audio amplification, the tubes
> have to be in pushpull in order to reproduce both halves of the sinewave.
> Thus the well-known "class B modulator" came into being.
> Interesting that you mention this Don. I just read where it was Art Collins 
> and his group that came up with the idea of using Class B push-pull audio 
> for Class C rf amplifier. I'm not a Collins aficionado but Joe, N3IBX gave 
> me the book, "The First Fifty Years of Collins" to read and I found it very 
> good reading. There was some self-promoting in there but I was mildly 
> surprised when I learned Collins did discover the Class B P-P plate 
> modulation scheme.
> Mod-U-Lator,
> Mike(y)

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