[R-390] R-391 stuck slug screws

[Mack McCormick]

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
>