In an article on IMD and splatter, tech guru Rob Sherwood noted that the cleanest tranmitter he had ever owened was the Colling 32S-3. Here is the article. https://soldersmoke.blogspot.com/2024/09/sherwood-its-time-to-clean-up-our.html
In it, you will see thar Rob has the spectrum anayser two tone test to prove his point.
This got me wondering: Why was the Collins transmitter so clean. Today I looked at some ot the tech info on this rig. I think I have found the answer. The Collins Collectors Association has a great page on the 32S-3: https://collinsradio.org/cca-collins-historical-archives/the-equipment-of-collins-radio/the-grey-boxes/32s-3/
The key lines are these:
Click on the paragraphs or go to the link for a clearer view
I think the explanation of Collins'32S-3 cleanliness is due to 1) Thermatrons in the final stages and 2) Negative feedback to take down any IMD products that might appear due to non-linearities in the finals.
There is nothing magical in that technique. Heck, we could homebrew that today. We could build HDR stations (perhaps transistor-tube hybrids) that would be cleaner than their commercial SDR cousins.
I too have always owned Collins 32S's. That transmitter ALWAYS gets great comments on the audio. On Sundays, on the Collins Collectors Net, it is easy to tell the difference in the audio quality of the guys using a 32S, and someone that checked into the net with a Icom/kenwood thingy. No contest.
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