[R-390] Cleaning Potentiometers

[Peter Worrall, G4GJL]

Just a two cents worth comment..............

I have rebuilt 5 R390As. from the St Juliens Creek Massacre.

 With one exception all had dirty audio pots, which I cleaned with 
lubricating switch cleaner.

However one further problem is that the ohmic value of these pots increases 
with age ( and this would apply to any set, St Juliens or not), so I got 
nice clean noise free pots, but still with rather raspy and poor audio.

I ended up replacing most of them with new pots of the correct ohmic value, 
this brought the audio back to life.

The above action was taken after replacement of the plug in electrolytics 
with modern fresh in-fills,which in itself brought about a marked increase 
in audio performance

Pete
G4GJL
----- Original Message ----- 
From: "Brad Huff" <huffb at avalon.net>
To: <r-390 at mailman.qth.net>
Sent: Sunday, July 10, 2005 6:03 AM
Subject: [R-390] Cleaning Potentiometers


Hello,
I apologize if this has been discussed before but sometimes it's the simple 
things like this that can cause us the most trouble. What are you guys using 
to clean and take the noise out of carbon potentiometers? I've heard horror 
stories about the different brands sold for this purpose. I've even heard of 
the value of resistance changing after using some cleaners, this in fact has 
happened to me and I'm still waiting to see if it will return somewhat to 
what it was before cleaning. I've been told that the stuff Radio Shack sells 
is not good for carbon pots and that the mineral oil in it will attack the 
carbon element. Any thoughts?-Brad
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