[Hallicrafters] restoring yellowed clear plastic fronts onSX-100 & SX-96 S-meters

[Richard Knoppow]

----- Original Message ----- 
From: "Gerry Steffens" <gsteffens at bevcomm.net>
To: "'Brian'" <cosmophone at yahoo.com>; "'Richy'" 
<ss409ss at aol.com>
Cc: <hallicrafters at mailman.qth.net>
Sent: Thursday, March 27, 2014 9:26 AM
Subject: Re: [Hallicrafters] restoring yellowed clear 
plastic fronts onSX-100 & SX-96 S-meters


> Thanks for the words guys.
>
> I have been restoring and collecting since the late 1960s. 
> I have tried the
> Novus and the Meguiar's stuff (Novus 1,2 & 3 also 
> Meguiar's 10, 17, 18) to
> little or no avail.
>
> Since I also do classic cars, I have used the headlight 
> restorer on some
> plastic lenses that had deteriorated down to translucent 
> as opposed to
> transparent.  It seems to work on those extremely yellowed 
> lenses and thus I
> wondered if anyone had tried it on Halli S-meters.  At 
> this point I am a
> little hesitant to risk any of my good meters (I sold off 
> the marginal ones
> - chips or cracks, etc,) which are all in radios.
>
> I am a collector and I have approaching a dozen Hallis 
> (out of about 34)
> that need treatment.
>
> Thanks for the input.
>
> Cheers,
> Gerry
>
     AFAIK, Novus is just an abrasive polish and I think the 
headlamp cleaner is the same. The problem with these dials 
is a from a chemical change in the plastic itself. The 
yellow stain is not on the surface, its throughout the body 
of the plastic. If you polish you may get some yellow stuff 
on the cloth but that will be only the stain at the surface. 
I have read, but never tried, that stain can be removed by 
soaking the plastic in a solution of oxygen bleach while 
exposed to direct sunlight. There have been a number of 
reports that it works. I am now drawing a blank on the name 
of the process but a Google search may find it. If the dials 
in question have printing on them I would be careful because 
it might not survive the bleaching process. Actually, it 
would not survive abrasive polish either.
    I have no idea of what effect the bleach might have on 
the plastic. There were many plastics used as dial material 
including acetates and some will be affected perhaps 
becoming very brittle or shrinking up when dried again. It 
would be helpful to have something expendible to test with.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com