[R-390] Why polished radios?

[Tisha Hayes]

I think that with aluminum the passivation layer reforms in a matter of
seconds. If it is not exposed to a corrosive atmosphere or an electro
galvanic reaction it does not go any further.

I use a metal polish with a cloth wheel to clean up things like IF cans in
an SP-600 or brass gears for drivetrains and it contains some sort of
protective layer like a wax. I have never thought of doing it to an entire
chassis and would think that taking down all of the anti-corrosive coating
on an R-390 would be quite an exercise.

Is the yellowish color a chromate coating? I would not want Erin Brockovich
to show up at my door because I used hevavalent chromium to restore a finish
and dumped the residue down my septic system. For a shiny radio you may be
able to use a lacquer varnish to lock in the pretty look or if you really
wanted to get into it you could completely strip the chassis, take out all
of the components, tube sockets and steel parts and anodize the entire
thing. You can even do anodization in colors (Caswell kits). It would take
some pretty serious solvents, strippers, acids, etc.. to get down to bare
metal. I would probably go with the anodized gold color <s>.

Maybe we can simulate the yellow chromate color by putting the radio in the
same room as a dozen smokers for a year <j/k>.

I have seen some industrial equipment in shiny aluminum cabinets put in
places where they were eaten up in weeks. At water plants where there are
high levels of chlorine, fluorine or ozone gas or in salt-water environments
like on the pier at Pensacola NAS. It is amazing how quickly ozone eats
stuff up and leaves nothing but a black sticky residue behind.

Anodization is actually an insulating layer and I could see problems where
tube socket screws need to get to chassis ground. Then again, slight
differences in alloys can also cause dissimilar levels of anodization and
you could end up with a very grainy, porous finish on external surface areas
and almost no coating inside of the little cavities inside of something like
the bottom of an IF deck.

I DESPISE the cadmium coated screws in a receiver like the SP-600. Almost
every one of those things looks awful. I went through a small fortune in
stainless steel hardware to replace those things.  Pulling stuff apart to do
a re-cap; old screw into the trash can, dig out a new shiny philips head
screw, washer and nut in it's place. It is amazing how many intermittent
problems on a receiver can be caused by loose hardware.

-- 
Ms. Tisha Hayes/ AA4HA
-
*"Learning is not virtue but the means to bring us an acquaintance with it.
Integrity without knowledge is weak and useless, and knowledge without
integrity is dangerous and dreadful. Let these be your motives to action
through life, the relief of the distressed, the detection of frauds, the
defeat of oppression, and diffusion of happiness."  -- Nathanael Greene*