On 17 Feb 2013 19:22:20 GMT, wrote:

I'm repairing an old italian stereo amplifier and the volume dual
potentiometer is scratchy beyond any hope. I tried cleaning it and then
also dismantled it but the carbon part is too much ruined with several
pits. Also the two channels doesn't really track anymore, having large
differences in resistances in almost all positions.

I've fixed pits and burns on pots using conductive silver ink, also
known as PCB repair. The action of the pot will not be perfectly
smooth, but at least it will not be going open circuit over the pits.

If you want to do it perfectly, you can mix flake graphite (available
at the auto supply store as a lubricant) with glue to make something
more like a resistor. Be sure to get flake, not "powdered" graphite
as only flake is conductive.
http://www.kobakant.at/DIY/?p=634

The problem is that these potentiometers (47Kohm) have an extra fourth contact
which is at fixed position at 10K from one end. It's the first time I see
such a potentiometer with fixed divider. Does anyone know how to source
a suitable replacement?

I haven't seen one of those since the 1960's.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558