[ARC5] R-25 dial nonlinearities

[Glen Zook]

I am trying to remember the "other" company that made the tube-type LMOs.  There were at least 2-other companies that made the solid-state LMOs and a lot of those units did not "track" properly between the 100 kHz points whereas the TRW LMOs were always within the 1 kHz calibration across the entire 500 kHz of coverage.

 Glen, K9STH 
Website: http://k9sth.net

      From: Kenneth G. Gordon <kgordon2006 at frontier.com>
 To: ARC-5 List <arc5 at mailman.qth.net> 
 Sent: Sunday, January 8, 2017 4:53 PM
 Subject: Re: [ARC5] R-25 dial nonlinearities
   
To put another possible technique in "the pot", I found it very interesting that the Heathkit LMOs, used in their SB rigs, all of which exhibit very linear tuning, use a very small portion of the main tuning capacitor to cover the required range of 500 kHz.
I would guess it to be less than 1/4 of the total available capacitance range. The capacitors are very, very well-made, but the plates don't look to have an unusual shape either.
I have noted this as something very interesting, but have not yet investigated it to see if I could learn why they did this, and how the very nice linearity occurs.
The LMOs were never made by Heathkit, who bought them from two companies, one of which was TRW, and I cannot remember the other one. Perhaps Glenn Zook can tell us.
Most of those LMOs were tube-based, but the last one, that in the SB-102, was solid-state.
I also found it interesting that the article posted by Clare includes a capacitor from an ARC-5 transmitter's VFO.
Which reminds me: do we yet know for certain that those capacitors were made with Invar, which is inherently temperature-compensating?
We DO know that the ARC-5 transmitters' VFO capacitor is very, very much different from the other two capacitors in the transmitter.
I was told once many years ago that they were made with Invar, but have never seen anything definitive written on this subject.
   
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