[R-390] Knob finish

[Barry]

Hi Francesco,

That yellow-ish finish is a zinc chromate conversion coating.  It prevents the aluminum from oxidizing as much and allows it to take paint much better.

The original paint is quite hard to remove.  If some are easier, then it's possible someone has already repainted them.  Someone may also have had them powder-coated which is very difficult to remove.

I found it easier to just use a wet-or-dry silicon carbide "sand paper" and remove the paint down to the bare metal then prime and paint.

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: fdigio1 at gmail.com
> To: r-390 at mailman.qth.net
> Sent: Saturday, March 30, 2019 6:37:44 AM
> Subject: [R-390] Knob finish
> 
> Hi everyone,
> 
> my project of restoring my R-390A goes on.
> 
> Now I am dealing with the front panel knobs. Many of these are scratched,
> 
> so I decided to strip away the old paint and redo the varnish.
> 
> It's been a surprise to me. The paint of some knobs  treated with paint
> stripper,
> 
> go away without effort.
> 
>  
> 
> With the others, it is very difficult to remove the old paint.
> 
> These knobs have some light differences from the others.
> 
> They have 3 light "dimples on their base
> 
> (the side facing the front panel).
> 
> After several hands of paint remover, the original paint is still there.
> 
> Where the black paint is not present, the surface of the bare aluminum is
> light yellowish,
> 
> similar  as the surface of the rx's mainframe.
> 
> The varnish of the "three dimples knobs" is extremely resistant and durable.
> 
> Aside the difficulties to remove the paint, I wander what kind of finish the
> knobs have?
> 
> What magnificent piece of equipment the R-390 and R-390A are!!!
> 
>  
> 
> Regards
> 
> Francesco Di Giovanni - IN3XZP
> 
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