Finding equivalent electronic repair components.

I have a microscope who’s power/brightness potentiometer has seized up. I have been looking for a suitable replacement on Digikey, Mouser, et al but haven’t been able to find anything even close. It’s a 100K linear pot with a 5/8" slotted shaft, 1/4" diameter with a built in DPST switch. I found a company that will assemble one to spec from modular parts, but they want around $150 in set up and item costs. The original vendor (Noble) doesn’t make it anymore, and it seems that size is also generally unavailable. Am I missing something? Has the general trend toward small devices moved supply away from these larger parts?

Maybe you can find originals at aliexpress.

Farnell has 100 different 100K pots.

How about:

The dimensions aren’t making sense - the shaft is a larger diameter than the body of the pot? And it really needs to be a DPST switch? That puts you into oddball parts territory. Most pots with switches are just SPST.

Noble appears to be a European maker, for whatever that may be worth.

Mouser has a squizillion or so options made by Vishay. Mod-Pot is another brand of modular pots - I suspect the people who quoted you $150 are charging a steep nuisance fee for probably ten bucks worth of parts.

Worst case scenario - can you find a 100k linear pot that fits and wire up a separate switch?

The only sticking point is the DPST really - and does it actually use the other pole? Hard to imagine what it could be used for.

You need to probably list out all the specs more carefully. It is pretty rare you can’t work out a replacement. Even if you have to get a new knob for the shaft, or take to the shaft with a hacksaw.

A lot of pots have quite small bodies now, but retain the standard mounting hole and shaft size.

The problem with the custom build pots (like Allen Bradely ModPot) is that they tend to have a minimum quantity or a setup fee. And indeed, it is mostly to discourage lots of one off requests.

You might be better off finding another one to cannabalise

Yeah. Is there some reason it needs a 2-pole switch? This sounds like some type of hospital grade safety design that switches both lines of the power cord. Wiring the neutral wire direct and switching only the hot side will be fine in 99.9% of usage. Also, don’t get too picky on the exact shaft configuration.

This guy may be a little slow in response but he assembles custom controls for obscure antique radios, often from NOS new parts.

Get a printed catalog from Mouser or Digikey. For me, anyway, it is difficult to search for certain components on a web page. In my experience, switches are sold separately and piggy back on the pot, ie, bend the tabs, pull the cover, add the switch and bend the tabs back.

PS - Are you searching for 1/4" shafts? Most pots made in the last 20 years are metric with 6mm shafts. They usually fit OK and you can cut a strip of aluminum from a pop can to use as a shim to center a 1/4 knob.

Digi-Key: Bourns.
What power requirements do you need?