[Boatanchors] 85 kHz transformers

[Dave and Sharon Maples]

Bill: That's wonderful.  Please let me know the price of shipping.

Thank you VERY MUCH!

All: The Q6'er appeared in an Australian magazine back in the fall of 1960.  Basically the author took six of the 85 kHz transformers and operated them in pairs.  He had a product detector, BFO, and AM detector in the system.  Overall it seemed very nice.  I imagine it was highly selective, but the adjustment of inductor spacing and stagger tuning might have allowed him to create a very customized SSB filter with a very good shape factor.  There is one page of the article out there in Internet land: https://worldradiohistory.com/hd2/IDX-AUSTRALIA/IDX/Archive-Radio-and-Hobbies-IDX/60s/Radio-and-Hobbies-1960-12-OCR-Page-0033.pdf  I hope to be able to spring for the issue of Radio, Television, and Hobbies that had this in it so I can see the full spread.

What I plan to do is measure one of the 85 kHz transformers on the bench and document its selectivity at both coupling points, and from there try to estimate what a Q6er or similar design might deliver.  

I got curious about these IF cans.  Apparently to resonate around 85 kHz with a 180 pf capacitor the coils have to be around 19.5 millihenries.  Murata Power Solutions makes an inductor (https://www.mouser.com/ProductDetail/Murata-Power-Solutions/17226C?qs=sGAEpiMZZMv126LJFLh8y6ElRBzbBTips6jRdwtJxGI%3D) that is 22 millihenries and has a Q of 100 at 50 kHz.  It seems like mounting one of these on a moving PCB so it is lined up axially with another one that is fixed might allow reproducing the variable-bandwidth tuning arrangement.  The coils are cheap (less than $1.25 from Mouser).  They are also quite small (just over 0.25" diameter) so it might be possible to build some low-frequency bandpass filters with fixed adjustments that would fit nicely inside a BC-348.  I may pick up a couple of the coils just to see what they would be like coupled that way.

The Hammarlund HC-10 is horrendously expensive and hard to find, but it occurs to me that it might be possible to come up with something that provides similar functionality for a lot less cash.  The result won't be the same as an Icom 7300, but it would still be fun to examine.  Setting up something like a Q6er with a mixer stage in front of it and a LO that could adjust with a vernier +/- 5 kHz around the desired IF frequency to be downconverted from could be handy with R390s, BC-348s, and even Command sets.  The same chassis could have multiple inputs and a switched mixer to allow any of the receivers to be brought in and passed through the system.  Each receiver would be responsible for its own AGC up to the point the IF signal left the receiver, and this thing would do AGC processing for the downconverted IF.  For very-high-quality AM reception an infinite-impedance detector or a precision full-wave rectifier might be part of the design.  It might be built with vacuum tubes or with solid-state devices.  

Not sure which year I'd be able to finish this 😊, but it might be interesting.

Thanks,
Dave WB4FUR
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