As my aftermarket knee proves, this topic applies to both instruments and people, so this should cover a lot of ground.

Here in Ohio we have almost NO place to take in a knob to find a replacement because you lost 2 of the other knobs. Radio Shack, and Olsen's way back, were the go to places, but Radio Shack is gone. Plus, how do I order knobs online? I don't know what to measure and how to describe what I need to some clerk on the phone that was not yet born when the Korg KMX-62 rack mount mixer was made that needs 7 new knobs because not only is one missing completely, the rest of them (6 channels and a master volume) are missing the little center disc that has the index mark on them. I have zero idea how I am going to find knobs. This mixer is from 1988. And funny story, I bought it in 1988. In 2017 I used it (and the matching EQ) as trade collateral for a case that was the right case for my Applause acoustic. That guitar and case went to the same local shop for resale, and when it was sold I got enough money for them that allowed me to buy the rack pieces back from the guy and get a used 6 space rack in the deal. I can't even wrap my head around if that was win, lose or draw on that deal that spanned 4 years.

Radio Shack, how I miss thee.... There used to be one every 37 feet. Now the places that have a Radio Shack signs just have a handful of stuff with their labels. AND there's no guarantee they ever had this exact knob. Where's Billy at? He's a builder! Where do I buy parts and what do I have to measure?

Guess what I am doing tomorrow? Going to places to get suggestions where to look for these knobs. It may be as simple as asking the people where I am taking the mixer to get the stereo pot that snapped off WAY back when replaced. Thanks, roadies...

Check e-Bay for a "parts only" donor mixer or replacement knobs from someone parting one out.

If you have at least one knob, measure the inside diameter where the shaft goes, the diameter and height. Then search online for a knob with similar dimensions. The shaft dimension is the biggie as it may be metric (likely) or SAE (unlikely). But try to force a knob with the wrong internal diameter will either cause damage to the shaft or you won't be able to tighten the knob. Most knobs are press on, not held on with a set screw. Shafts may have a spline to them or split. Press on knobs work real well with spline shafts.

Believe it or not, you may be able to find generic knobs that will fit from the hardware section of Lowes Hardware or Home Depot.

Online search at +++ Digikey +++ , +++ Stewart Mac +++ , +++ AllParts.com +++ , +++ AliExpress +++ , +++ Amazon +++ .

While you may not find the exact knobs you may find replacement knobs that work as well, or look even better, then the original.

These are spline shaft knobs. I think an early stop will be at Home Depot where I will "demo" a micrometer so I can measure the ID of the knob. The thing about this is that picture shows a "center" knob that slides down onto the spline and seats onto a second knob because the back control is for the effects return.

Here's a look. Stereo!

Actually Eddie, a competent electronics person would be able to provide you with what you need if it exist.

He would need Make, model, a serial number. He then may be able to find a schematic and perhaps a parts list.

I would likely find the item from CE Distribution, DigiKey or Mouser electronics. Perhaps on ebay also. Ebay may sell the whole unit as parts which is where really hard to find items often come from. (the Cheap answer)

Two or three places in Europe collect hard to find items and sell for large amounts of money. So do a few other electronics places but they would be unlikely to take your call if they don't know you. (expensive)

Then their are electronic/ mechanical engineer types who have the equipment to make a new one. I can make you a knob in any material with gold or silver or any type of plating to include amorphous diamond carbon using a high vacuum gas plasma reactor. ( only if you are Elon's brother with plenty of $$$)

Home Depot?....good luck on that

Now...lets get back to your issue. If you don't need everything to match and only function, try ebay first. They sell assortments of knobs. The sell push pull pots. I most likely have everything you need but I have to have the defective parts in my hand and Make, model and serial number of the unit. Some internal photos would help.

Billy

EDIT: The tool to measure with...$20 at Harbor Freight

Billy, the broken pot will get handled by my guy. I just need knobs that have the small center insert that has the index markings. Purely cosmetics. If my guy (Jim) can source them, I will happily et him! I'll see him tomorrow. If I have to source them I need to go to a DIY store and "test" a micrometer so I know the diameter of the hole in the knob.

The broken pot in the picture isn't push push. It's just a stereo pot and the inside ring goes to the effects bus. A roadie snapped it off one night putting my rack away.

And he lived!!!

Finding a knob "may" be a problem. There are two or three ways to solve the pot issue.

This knob controls two separate functions, VOL and Effect.

So I read what you said again and I assume the knob is split and the outside part holds the inside part on.

Billy

That is close. The bigger piece slips tightly on the erect return ring. It will stay on without the center knob. Worst case is that I only find the slimmer center knob and I don't use the effects loop anyway. I'll know more Monday morning.

My gut response would be to check with a place that sells ham radio equipment. Or a ham...

There is a lot of old radio equipment out there and hams save pieces and parts.

...Deb

These days, any geek with a 3D printer can make you a replacement knob for old equipment.

I miss Radio Shack and also Mom & Pop music stores.

People started buying from Internet, Mail-Order, and Big Box stores to save a few pennies, and the expert people we used to depend on went out of business.

We did this to ourselves.

Good luck with your knob quest.

Notes

You might find a generic Dual Concentric Control Knob that will work.

Here's an example:

Dual Concentric Knobs on Reverb.Com

-rob

My guy has the mixer now and he said he probably has knobs laying around.

Does everybody have "a guy" like how everybody says their doctor is "the best"? "You gotta go to my guy. He's the best!"

I'll never forget the joke "What do you call a guy who finishes last in his class in med school?"

"Doctor..."

Worst case I told him that f he had to order them to do so. He can measure the shaft sizes and stuff.

Danelectro...

Man if you gotta use a pipe wrench to turn the knobs maybe it's time to put some lubricant on them.... I broke a tuning peg on my very first guitar doing that very thing.... some grease would help.

But yeah...Amazon or Ebay will get you there.

LOL @Herb's comment!

The top picture is actually one that HAS a knob! It's just that I bought that mixer in like 1988. The second pic is the one the roadie hit on the end of the stage and snapped channel 4 off. The knobs are on the end of the broken spline in a bar somewhere in Canada.