David Forsyth wrote:

I have a need to rebuild some slide pots from 1970's musical equipment
that
have worn-through resistance strips. The pots are long since unobtainable
(made by CTS), and I have yet to find any suitable replacements. The
resistance strips inside the pots are removable, and consist of a die-cut
non-conductive substrate onto which a carbon resistance compound was bound
and on which the slide contact of the pot slides. Each end of the strip
has a metal connnector crimped to it to serve as an end terminal for the
pot.

I think if I knew what kind of binder and process is commonly used to
adhere
the carbon to the substrate I could restore the resistance layer. It
would
most likely have to be baked onto the strip, which is not a problem. For
the resistance material itself, I was thinking of using material from
carbon comp resistors (it would be trial and error to find the right value
for this
application). So, I am trying to find information on how resistance
material is bound to a substrate for use in wiper/pot applications (it
would
have to be fairly resistant to abrasion, solvents, etc.) Please email
foda01 at epix dot net with any helpful info.

thanks,

Dave

If these instruments are to be sold to the public then I agree with the
others that you probably should make an obtainable pot fit and adapt the
mechanical parts and circuit as necessary, because home-made pots will
quite likely wear out quickly and your customers may not feel like they had
their money's worth.

If you do feel like making your own pots anyway, I wonder whether you might
find that black conductive ESD-safe bags are suitable, at least for
short-term use. In the UK at least, Farnell sells chips packed in black
bags which I think are made by Vermason and are marked PE-LD. In my
experiments I have found that if you cut a strip from one side of the bag,
the strip of plastic seems to be made of three layers stuck together. Each
surface of the strip is conductive but both conductive layers are insulated
from each other.
http://www.vermason.co.uk/products/p...e_flexpack.asp
If the resistivity is right then you might be able to glue a layer into your
pots. It is probably not easy to glue it in a permanent way. So basically
the material is conductive on both sides but if you wiper is on the top
surface then the end contacts need to be on the top surface also.

Making pots with a taper slightly different from linear should be easy
enough provided you can fit a strip of plastic which has a width that is
not uniform along the track.

Chris