James Rockwell's Cathanode Amplifier Topology

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mediatechnology
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James Rockwell's Cathanode Amplifier Topology

Post by mediatechnology »

I just found this fascinating article on James Rockwell's Cathanode Amplifer in Radio World.

Could this have been the first "switching" amplifier?

Rockwell devised a way to reduce the tube count to four by shifting the alternate (“bottom half”) cycles, which would normally be handled by the lower half of a Class B circuit, back to the same tube that amplified the “top half.” While this sounds a bit like single-ended Class A operation (and Rockwell’s circuit used only one high-power triode), it wasn’t. He employed a couple of small triodes and two rectifiers as a means of “switching” alternate half cycles to the big tube (which was biased for Class B).
https://www.radioworld.com/columns-and- ... hanode-rig

Image
Cathanode Amplifier US Patent 2233961 Figure 1 1939.

Class B Modulator: http://www.google.com/patents/US2233961
Cathanode Bridge Amplifier http://www.google.com/patents/US2817718

After looking over Rockwell's patents I agree with Radio World's author that Rockwell appreciated symmetry.

More here: http://arizona-am.net/WLW/Docs/index.html
emrr
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Re: James Rockwell's Cathanode Amplifier Topology

Post by emrr »

Nice article link, I missed that one. Now about those mercury arc rectifiers...
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JR.
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Re: James Rockwell's Cathanode Amplifier Topology

Post by JR. »

Switching? :lol:

It is interesting to see the cost engineering dynamic. Back then it was cheap to throw an extra transformer at it to reduce the relatively expensive active device (tube) count.

I recall back in the '60s seeing an early solid state amp that used interstage transformers just like an old tube amp but with early PNP power devices in place of the tubes.

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mediatechnology
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Re: James Rockwell's Cathanode Amplifier Topology

Post by mediatechnology »

Back then it was cheap to throw an extra transformer at it to reduce the relatively expensive active device (tube) count.
In the AM modulator work he did he actually eliminated the plate modulation transformer and used the audio Class-B amp to drive the plate voltage supply transformer. So he eliminated both half the modulator tubes and a big chunk of iron.
“He wanted a transmitter with very low distortion,” said Haehnle. “None of the available models came close to meeting his requirements, so he set about to design and construct something that could. One of the things he wanted to accomplish was to eliminate the big plate modulation transformer, as he saw this as a source of distortion.”
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