OK, I see now what the circuit looks like, in the manual. The pot is
used in rheostat mode, so the specific value is needed, and it would
take some more modification of the circuit to increase the setting
resolution.
I would recommend making a simple change to the existing pot hookup
though, which is to tie the "NC" end of the pot to the wiper - I have
this thing about not leaving dangling ends on pots used as variable
resistors. The most likely possible failure mode in a pot is an open or
intermittent wiper. In this circuit, if the wiper should open for some
reason, the circuit will go open-loop, and self-limit at around 13 mA
through the coil (or somewhat less if the coil's resistance is higher
than 700 ohms or so) - twice the normal maximum setting, or four times
the power dissipation. I don't know if this matters here, but for higher
reliability, tying that pot's loose end to the wiper will ensure that
this can't happen - the circuit will limit at the maximum of the normal
adjustment range.
Ed
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