[R-390] R-390 Digest, Vol 255, Issue 16

[Mack McCormick]

Bill,

Thank you. I'll try some of that blend.

73,

Mack
W4AX
https://www.qrz.com/db/w4ax


On Mon, Oct 27, 2025 at 12:00 PM <r-390-request at mailman.qth.net> wrote:

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> Today's Topics:
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>    1. Re: R-391 stuck slug screws (Mack McCormick)
>    2. Re: R-391 stuck slug screws (Bill Blodgett)
>
>
>
> ---------- Forwarded message ----------
> From: Mack McCormick <w4ax.mack at gmail.com>
> To: R-390 Group <R-390 at mailman.qth.net>
> Cc:
> Bcc:
> Date: Sun, 26 Oct 2025 16:59:12 -0400
> Subject: Re: [R-390] R-391 stuck slug screws
> Here’s an update. Each one of the tuning shafts was sealed with some type
> of sticky black substance similar in action to Loctite. The only solution I
> found was to use a micro torch and heat the slug while gently turning it
> until it broke free and then using a wire brush to remove the gunk. Is it
> possible the depot used some sort of Locktite substance so the tuning did
> not drift during vibration? In any case that tuning slugs are free now.
>
> 73,
>
> Mack
> W4AX
> https://www.qrz.com/db/w4ax
>
>
> On Sun, Oct 26, 2025 at 10:33 Mack McCormick <w4ax.mack at gmail.com> wrote:
>
> > I'm repairing/aligning a R-391 for a friend. Every single RF deck slug
> > tuning screw is solidly stuck. I think it is a galvanic response between
> > the brass and steel.
> >
> > Does anyone have tips to free the slugs? They won't budge using a
> moderate
> > amount of force. I've used PB Blaster and heat to no avail.
> >
> > I've repaired at least one hundred 389/390/390a/391 over the years but
> > this is the first one I've encountered with every slug stuck.
> >
> > Thanks in advance for any ideas.
> >
> > 73,
> >
> > Mack
> > W4AX
> > https://www.qrz.com/db/w4ax
> >
>
>
>
>
> ---------- Forwarded message ----------
> From: Bill Blodgett <whb5k at icloud.com>
> To: Mack McCormick <w4ax.mack at gmail.com>
> Cc: Group R-390 <R-390 at mailman.qth.net>
> Bcc:
> Date: Sun, 26 Oct 2025 19:12:05 -0500
> Subject: Re: [R-390] R-391 stuck slug screws
> Years ago a machinists’ magazine performed scientific comparisons of
> commercial penetrants advertised to be useful in obtaining release between
> “stuck” mechanical items.  Included was a test of a “home remedy” of 50%
> acetone and 50% automatic transmission fluid.  FWIW, PB Blaster released
> better than WD-40, but that’s not saying much.  The hands down winner ? ….
> the 50-50 mixture of acetone and transmission fluid.  I’ve made this up
> with synthetic auto transmission fluid, in one instance, and non-synthetic
> auto transmission fluid in another.  I did not perform a scientific torque
> release test, but suspect that using the synthetic fluid may work the best
> because it should have smaller molecules.  Please note that whether you use
> the synthetic or non-synthetic auto transmission fluid in the mixture,
> either will separate from the acetone unless you shake it up and apply it
> quickly thereafter.
>
> Of course, if there is actual corrosion causing the issue with the slugs,
> that’s a different issue probably not solvable with a penetrant.
>
> Good luck & 73,
> Bill
> W5WHB
> ++++++++++++++++
> Bill Blodgett
> Arlington, Texas
>
> > On Oct 26, 2025, at 9:33 AM, Mack McCormick <w4ax.mack at gmail.com> wrote:
> >
> > I'm repairing/aligning a R-391 for a friend. Every single RF deck slug
> > tuning screw is solidly stuck. I think it is a galvanic response between
> > the brass and steel.
> >
> > Does anyone have tips to free the slugs? They won't budge using a
> moderate
> > amount of force. I've used PB Blaster and heat to no avail.
> >
> > I've repaired at least one hundred 389/390/390a/391 over the years but
> this
> > is the first one I've encountered with every slug stuck.
> >
> > Thanks in advance for any ideas.
> >
> > 73,
> >
> > Mack
> > W4AX
> > https://www.qrz.com/db/w4ax
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