[R-390] Main Dial Tuning Friction

[Larry H]

Ed, You can try doing the recommended PM from the tm-11-856a on p. 150, but
after all that time, it probably won't help that much.  The 3 areas that
put load on the kc tuning knob are the vfo, gear train, and the slug
racks.  You can try to identify which is doing it by the process of
elimination.  Try to disconnect the vfo at the oldham coupler,  Try
manually raising up the slug racks one at a time when one is at the bottom
of travel and see if it's sticking (be careful to not go too high).  I
usually find them to be a problem.  If you determine that the gear rack is
part of the problem, cleaning and lubing without taking it apart rarely
does much good, and some times makes it worse.

A synthetic heavy weight oil should be used on the gears. Most automotive
oils will have that familiar aroma, if you like that.  There has been lots
written on this subject and is in the pearls in 'rf deck, mechanical'.
Link to pearls: http://www.r-390a.net/Pearls/

Have fun.

Regards, Larry

On Mon, Feb 25, 2019 at 3:34 PM Ed G <ed.n3cw at gmail.com> wrote:

> HI Folks,
>      Been following this list for many years, and appreciate the wisdom
> here. I have a Capehart R-390A in great shape. It works well and has no
> problems except that the main tuning dial (the “Kilocycle Change” dial) is
> somewhat tight…not excessively so, but a bit hard to turn.  I have cleaned
> the tuning mechanisms, and used Teflon grease in a few spots and synthetic
> oil sparingly on the gears.  Because the receiver is working so well I am
> hesitant to disassemble anything too far.
>      I’ve read lots of R-390 material over the years, but don’t recall
> seeing much about a recommended way to approach gear train friction so that
> one ends up with the smooth, almost effortless tuning “feel” I have
> experienced on other R-390As (other than a total disassembly/rebuild).
>      Perhaps there are certain problem areas in the mechanism that tend
> increase tuning resistance over time? Something I could address without a
> complete tuning module disassembly? Any recommendations would be
> appreciated.
> --Ed—
>
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