[R-390] Cleaning sealed pots?

[Cecil Acuff]

Hi John and Group,

        I agree with you John,  Deoxit was not meant for pots....and will
damage them over time.  How much time depends on the wear the pot has
experienced prior to treatment with Deoxit.

Options...MG chemicals makes a product called NU-Trol which has worked well
for me.  It's quite lubricating though....just a small amount covers it.  It
also has solvents for cleaning.

Another option that has worked well also is a product by GC electronics
called De-OX-ID.  Not to be confused with Deoxit.  GC's product has been
around longer as I understand it from the friend and owner of the local
parts store where I get it.  Remember the old Quietrol....worked great...I
still have a small amount...but have been told the GC De-OX-ID is basically
the old Quietrol.

RS also markets a small can of control cleaner...not sure how it works
though.

CaiLube is strictly a lubricant...mainly used for lubricating the sliders on
a mixer board.  Keeps them sliding smoothly.  It has no cleaning properties.
Don't understand it causing problems with a vintage pot unless it caused the
phenolic base to swell opening up a thin spot in the carbon trace...which
may happen with any of these...don't know.

Anyway...just some options to consider.  I wouldn't use WD-40...it gums up
rather quickly....And don't use the new reformulated Blue Shower  (not Blue
Stuff....abrasive tuner cleaner...Yuk!)....it melts some plastics....learned
the hard way on that one....melted a 70's audio pot into one piece.   It was
sold by another store as a suitable environment friendly replacement for the
old Blue Shower.  NOT>>>>  The old blue shower was good to use on pots....Oh
well..so much for environmentally friendly...

Cecil...


----- Original Message ----- 
From: "John KA1XC" <tetrode@comcast.net>
To: "R-390 reflector" <r-390@mailman.qth.net>
Sent: Monday, April 19, 2004 12:54 AM
Subject: Re: [R-390] Cleaning sealed pots?


> Don't use Deoxit for cleaning pots, it's a contact cleaner and is designed
> to dissolve metal oxides (guess what some pot elements are made of ) and
> leave behind a light lubricant. The R-390 pots are very susceptible to
this
> kind of solvent damage and of course I found out the hard way. I make a
> habit of measuring the pot elements before and *after* I work on them, and
> watched one of the front panel's controls double in value after I Deoxited
> it. :^(
>
> So the next time I decided I'll try some CaiLube, after all it's designed
to
> be used on controls, and after an extremely gentle application to the
> element of  a replacement used Limiter pot (500K) that I was preparing, I
> saw its value go from about 800K to 3 Meg after just a few rotations of
the
> control shaft. :^(
>
> The original Limiter pot I was replacing was completely shot, its element
> measured 75 Meg, almost not there. In the same radio the IF Gain pot on
the
> IF deck measured 10X greater than it was supposed to be; in each of these
I
> suspect solvent application as the cause of the damage.
>
> I don't know what to recommend as a good cleaner or lubricant now, it
almost
> seems like voodoo. Some audio guys swear by WD-40, and others swear at it.
> Other remedies I've heard included Vaseline as well as some kind of
silicone
> gel that also provides mechanical damping, and another fellow in one of
the
> radio newsgroups makes his own secret homebrew formula that he sells. One
> thing is for certain - always measure the part after treating it to see if
> its value was affected.
>
> Often the 390 pots are not just a little dirty but actually worn out. I've
> had a couple of RF Gain pots that were mechanically worn out at the 10
> o'clock position that they normally sit at; there was simply no more
> resistive element at that one spot.
>
> I'd definitely like to find a good replacement source for the Audio/Line
> pots, but 2.5K panel pots with .25" shaft and audio taper are near
> impossible to find;  if they were 5K it wouldn't be so bad.  I've actually
> thought of trying a dual 5K pot with all the connections paralleled.
>
> John
> KA1XC
>
>  > Good evening all
> >
> >
> > I am working on a R-390, with sealed pots for the AF and line gain pots.
> Both
> > are very erratic, obviously need to be cleaned, but, they are the high
> > quality sealed units. The quality is nice, but how do you clean them?
Can
> one very
> > carefully drill a hole through the side, with a bit of grease on the
bit,
> and a
> > drill stop, and then spray in a bit of Deoxit? They don't look like they
> > would be easy to disassemble either.
> >
> > Any thoughts would be appreciated.
> >
> > Randy
> >
> >
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