Hi Several outfits made pot set OCXO's for a *long* time. As far as I know there isn't any sort of premature end of life situation with those designs.
Bob On May 12, 2013, at 3:40 PM, "Al Wolfe" <[email protected]> wrote: > Years ago we were taught that it was poor engineering practice to use pots to > trim a DC value, especially if any appreciable current was to be drawn from > the wiper. (Probably true for any kind of signal on a pot) It seems that > current through the wiper would eventually erode away the material under the > wiper. This is true especially for set-and-forget applications. If the wiper > is used only as a voltage reference and very little current drawn then it is > probably OK for most situations. > > The above info is mainly for carbon and ceramic pots. Wire wound ones tend to > be somewhat more forgiving but they tend to be step-variable between the wire > turns. Often the sweet spot is between the steps and they aren't very useful > for fine tuning purposes. Sometimes we would use two pots in series. One was > set up as a rheostat and was around 5 percent of the ohmage of the main one. > It was used for fine tuning but the problem of DC current through the wiper > remains and is exacerbated. > > Probably the best design is to use fixed resistors for most of the voltage > divider circuit and the variable element be a small fraction of the total > divider resistance. > > Al > > >> Well, I decided to make the "Y" incision and pulled the circuit board >> out of the oven. (Photos later after I crop them.) >> >> Yes, the trimpot is part of the circuit associated with the thermistor. >> >> My plan is to check the resistors (surprisingly most are carbon film >> except those in the thermistor circuit), look at the circuit board under >> a magnifier, and stick it back in the foam for testing after making any >> repairs. >> >> Thanks again for the continuing comments and advice. >> >> Fred > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
