[R-390] Ferrite rod-slug and rack tuning assembly

[Alan Victor]

Thanks Tisha for the inputs and suggestions. I am just finishing up a
homebrew Utah plate just for the reasons you mentioned. I believe all the
slugs in the unit I have are fortunately in  good shape and I see no
binding in the slug-core interface. If there is any binding or hang up, it
would be the roller-rack interface as this is where most of the grime and
grease are hanging out. All of my ferrite slugs are clearly marked with
color coded painted dots. The RF slugs are unique as compared to the IF. If
I dare, I may take a homemade inductor, measure its L in free air and then
slide the R390A slugs in and calculate the effective permeability of the
core material.

I suspect my biggest fix will be the MHz gear-band switch tracking as the
symptoms for occasional loss of sensitivity point to this type of problem.

Alan

On Mon, Oct 20, 2014 at 8:55 AM, Tisha Hayes <tisha.hayes at gmail.com> wrote:

> I have never seen any sort of binding caused by the roller bearings on the
> slug carrier guides. They do such a minor amount of movement up and down
> when tuning ( less than an inch each ) that unless someone has done
> something physically damaging to the slug carrier guides they seem to last
> forever.
>
> Where I have seen damage to the slug carriers is when a radio was left
> sitting around without the Utah plate that covers the RF/IF decks.
>
> Those little springy pieces of metal attached to each slug are sort of
> fragile. If you do pull the slug carrier guide free (and that is where you
> unload those springs on the end that keep the carrier pulled down tight
> with the brass cams) you need to be careful to not break off a slug.
>
> If you pull a slug carrier out of the IF cans and you are missing a slug
> (because it has broken off) then you need to pull the IF can and dump out
> the slug or turn over the entire radio to get the slug to drop free. You
> "could" epoxy a slug back onto it's respective spring, that usually works.
> If not you can find a spare slug off of a surplus RF deck and replace it.
> Take care to note how far the slug is mounted into the rack (measure the
> distance) and try to replicate that insertion length. Because of the slight
> changes in permeability of the slug you will end up realigning the entire
> band. Just accept that inevitability and move on.
>
> As has been stated, you cannot use an RF slug in an IF spot (or vis versa).
> Also there may be some differences between slugs in certain spots (I am not
> too sure about that). The slugs are pretty sensitive to lots of things, too
> much cleaning, the use of lubricants or solvents, moisture, etc...
>
> The most I have ever done to them is to wipe them down with a little bit of
> isopropyl alcohol and to clean out the RF/IF transformer bore with a cotton
> swab. If I have one that scrubs against the wall I will dust it with talc
> (baby powder, extremely tiny amount). The other choice is to try to bend
> that springie thing that the slug is attached to and that is a very quick
> way to break it off. I found one RF deck where some individual (use
> unspeakable and impolite phrases here) used oil in the transformers. It
> made a big mess and turned things into a dirt magnet.
>
> --
> Ms. Tisha Hayes. AA4HA
>
> *""It is not because things are difficult that we dare not venture. It is
> because we dare not venture that they are difficult." -Seneca"*
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