For future reference I had a go at adapting one of the linear 250K ohm
slider pots. I doubt if the following could be used for the narrow tracks
inside the Chinese one, but if space allows for a more conventional one as I
had anticipated doing.
With 2 narrow pieces of "masking tape" I laid one, leaving just the outside
edge of the 250K track exposed and another one on the paxolin, leaving a 2mm
strip un-masked .
Squirted out some "RFI/EMI" spray into a pot and then with a toothpick laid
down a thin line of aquadag, or whatever it is, along about 40 percent of
the track (for comparison purposes) . Silver paint would have done instead,
but just a prooving exercise.
When dried that measured 23 ohm , over its length, and about the same for
that portion of the pot track via the 2 relevant terminals.
With a razor made 3 cuts, so divided the aquadag track into quarters. Then
some nail varnish just over the aquadag and onto the remaining paxolin just
to confirm no adverse reaction and a suitable fixative and rassembled.
I suspect the characteristic would be a bit wavy rather than linear, if
properly plotted out, but results
5 percent 10 ohm
10 % 400 ohm
20% 1.8K
30% 8K
40% 42K
50% 66K
and then much as the original 120K to 250K of course
I didn't bother with the following, but
For the upper section, for a log characteristic, then lay down a full length
aquadag track and make more , closer spaced cuts, and also a 1K and 20K
resistors or whatever , to fit, external to the pot.
Other non-linear characteristics , other than log could be so fashioned. And
as the thickness of the aquadag track is not critical then rotational pots
could be so converted almost as easily. The only criteria are higher ohmic
value to start with than final requirement, low wattage and enough space to
lay down these extra tracks.
Another one for my tips files. The internet timewasters can continue their
predilictions and buy 1000 off from Hong Kong or whatever they have to do.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/