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Potentiometer/Trimmer Ordering

Jamie Starr

Jamie Starr

Active Member
Hey Guys: I was wondering if anyone could offer advice or insight on ordering the correct physical size for pots and trimmers. I cannot tell you how many times I have ordered a pot or trimmer, only to find out that the terminals will not line up with the PC board I am working on. I have tried numerous times to measure the terminal holes on the board and then order the pot, with little success.

I am not referring to the value of the pot, i.e. 1k, 2.5k, ect. I am talking about the pot physically fitting my application. Thanks
 
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My advice is to check the data sheets. I've done the same as you, ordered a trimmer, and when it arrives it's the size of a pea, or smaller. Bournes multi-turn trimmers have to be adapted to go in the boards anyway, so I usually just use them.

Lee.
 
Bit of a loss here. The data sheets all give the pin spacing for the various patterns. Do you have a digital caliper? Even the cheapest will do for this job. Harbor Freight maybe? I'm a bit of a tool snob, but even these would work https://www.harborfreight.com/hand-...ter/6-in-composite-digital-caliper-63586.html A small ruler with a decimal scale will work if you can get it where you want to measure. Fractional is nearly useless so order something like https://www.amazon.com/PEC-Flexible-Stainless-Machinist-Engineer/dp/B00AG7XYF0 A 5R scale is a good choice. Or, use dividers to get the hole spacing, then measure the dividers. I'd probably make something before spending any money, but something like this is useful https://www.amazon.com/Navigation-C...ders&qid=1602099663&s=office-products&sr=1-11
 
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I have a dial caliper on my electronics bench. Battery has never gone dead. Dividers or spring calipers and a scale also work. They tend to be very cheap because they're "obsolete and useless" since it doesn't involve a battery and a microprocessor.

Most electronic component dimensions are in metric, but you probably won't need anything with finer graduations than 1mm.
 
You'll often find the manufacturer used some large open frame pot with a huge lead spacing. Even if you could buy one, it might not be a great choice. Look at the trace layout as you may be able to drill a small hole to accommodate a modern sealed pot with minimal fiddling of leads. It's usually not an issue with bias pots and such, but the intrepid service person should still check the voltage across the device and be sure to choose a replacement of sufficient wattage.
 
A divider or drawing compass is a great idea.

I find a digital caliper is too bulky/long/large to get right at the holes for a good measurement.

Sure, one could take out the part and measure but I usually don't like to pull parts until I have the replacements.
 
I will have to spend some time looking at data sheets. Most of the time I don't even get close enough to bend the leads. You go to Mouser's website and see 6000 pots....... a bit over whelming. Thanks for responses. I mostly work on Maratnz, so once I figure it out, probably the same size pots for most boards.
 
If there is space, maybe you can mount it upside down and run jumper wires to the board. I had replaced the volume control on a Pioneer SA-610. It was mounted on a small PC board by itself with jumpers down to the main board. I picked up a new pot and mounted to a small project PCB that I trimmed to fit. Worked great.
 
With components continually shrinking (in physical size) the jumper wire/adapter board approach seems to be more attractive. This is "old news" to many tube chassis restorers, since 2-watt pots 1¼" in diameter haven't been readily available for decades.
 
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