[ARC5] R-25 dial nonlinearities

[Ian Wilson]

Dubrow made a 689-BM128, but that's probably not what you are looking for;
Motorola perhaps (Cosmos, etc)?

73, ian K3IMW

On Mon, Jan 9, 2017 at 7:37 AM, Glen Zook via ARC5 <arc5 at mailman.qth.net>
wrote:

> 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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