[time-nuts] HP 5065 Rb update

[ed breya]

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