HELP - Seeking Replacement Balance Pot

[akacree]

Hello. I've been trying to find a replacement balance potentiometer for my Carver CT-3 preamplifier. I pulled it from the board. It’s an Alps. Maybe 3 pin + ground with a detent. Not sure what the bigger pin in the back is. Maybe for mounting securely(?) Either way, I’ve tried the Deoxit spray & twist route, tried researching online, and it seems it’s from the Alps RK097 series, but that doesn’t get me close enough to make a purchase with any confidence. I've attached some photos which should help. Ideally I can lean on some of you folks to guide me towards an exact replacement, since I'm having no luck through typical channels (Mouser, Digikey). Thanks in advance for your expertise, time & consideration.

 

[anatech]

Hi,
Have you checked to make certain there is no DC voltage across that control? A perfect pot will be noisy if there is any DC drop.

I was factory warranty for Carver and serviced those units. Never once had this issue.

-Chris

 

[Ixnay]

When I went looking for a balance pot, I felt lucky to have ended up with an Audio Note pot from parts connexion. Made to a higher quality than almost any other brand and works perfectly.

 

[anatech]

Hi Ixnay,
Was it for a Carver CT-3, and did it fit properly?

-Chris

 

[Ixnay]

No, sorry I didn't read that requirement right away from the post. A guy like me is more inclined to find the electrical value of the pot, say 50k for example, and then run leads if needed. Finding an exact replacement may not be so easy since once they get a new model of pot, the rest are left to fend for themselves on eBay or something.

 

[anatech]

It doesn't have to fit the PCB, you can run leads, but the shaft length and end style has to fit the knob. I think that one is knurled. I forget how long the shaft is.

Running leads may reduce channel separation, just keep that in mind.

 

[rayma]

"I've been trying to find a replacement balance potentiometer for my Carver CT-3 preamplifier. it’s from the Alps RK097 series"

It's a single pot. What's the resistance? Is there a center detent? Measure its dimensions out.
Go through the attached data sheet and generate a part number that will physically fit.
Then see if any distributors stock it. They may not.

 

[Ixnay]

What I am seeing is a D shaft. I suppose that the shaft diameter is 6mm since I see other specs in mm. This is where it gets a bit hard sometimes, and I have adapted different knobs and shafts to fit, but it is a bitch. When you are all done, you also have to see that it isn't out of square in any direction. Yup, best to find an OEM.
Don't know how much this will help but at the Carver Site there is a service manual available. The parts locator page may give some info and then perhaps parts list page too. It is a gamble, but it may help sort part of this out. Even though this is stated as a balance control, doesn't it look more like a sort of trim pots in that it only has 3 leads? I will take a look at the front panel at the site to get more acquainted with the unit.

 

[chrisng]

"104W" - Looks like it's a 100kΩ W-taper potentiometer.

 

[anatech]

It doesn't need the centre detent.

A balance pot (single wafer) is a linear control.

 

[akacree]

Have you checked to make certain there is no DC voltage across that control? A perfect pot will be noisy if there is any DC drop.

Thanks for your valued response, Chris. No - I haven't. Frankly, I wouldn't know how. When moving the balance pot clockwise, it would sound crackly out one speaker, while playing in the other, so I presumed it's the balance pot. Any further insight you could offer would be appreciated.

 

[akacree]

I forget how long the shaft is.

I've posted a photo, though I'm not sure what the industry standard is for how it's measured. The total length (bottom of threaded base to end of shaft) is a little under 1 inch.

 

[akacree]

What's the resistance? Is there a center detent? Measure its dimensions out.
Go through the attached data sheet and generate a part number that will physically fit.
Then see if any distributors stock it. They may not.

Thanks Rayma. I don't know the resistance/don't know how to measure it, but open to instructions & do have a DMM...
Yes - there is a detent. I've posted a photo with the measurement, but not sure what the industry standard is. Does the shaft measurement include the threaded base? Or just the shaft end to the start of the threaded base? If shaft only (no threaded base) length, then 20mm may be my reference.

 

[akacree]

When you are all done, you also have to see that it isn't out of square in any direction. Yup, best to find an OEM.
I will take a look at the front panel at the site to get more acquainted with the unit.

Agreed, and please do. Please let me know if I can be of more help in this process. I've attached a photo of the shaft diameter (sorry I don't have a digital caliper)
. Hopefully this helps...

 

[anatech]

Hello,
Before replacing the control.

Measure each terminal to common (ground) with a DC voltmeter, hopefully it can measure in the millivolt range. The readings should be zero or close to it. THey may drift a bit without the control in place. You are measuring on the board.

 

[rayma]

I don't know the resistance/don't know how to measure it, but open to instructions & do have a DMM...

Just read the instructions for your DVM to see how to measure resistance with it.

You can measure the shaft and bushing however you want, just compare apples with apples.
It's probably metric, as will be the replacement, so a micrometer would be best to use.

 

[anatech]

Yes, metric. The value is marked on the control.

 

[Ixnay]

Yes, a caliper would be most accurate. Roughly from what I see in the photo, it looks to be a 6.3mm/1/4" which was the common size back then. Carver equipment that I have worked on in the past is 1/4" shaft. You should look at the service manual at the 'Carver Site'. You may be able to get a better idea from it. There is a parts locator page, and then a parts list page as well.

 

[anatech]

Those were Chinese parts. It's metric.

No matter. Firstly, check to make certain you actually need to replace the part. Life will be much more simple if you fine another fault. If you go to the trouble of finding and installing a new one, you may well have the exact, same issue.

When you clean controls, it is the wiper in the centre that is noisy, not the carbon track!!!! Use a zero residue cleaner, and only a small shot into the centre. Cleaners all attack the protective grease, and shaft lubricants. The damage then occurs over time (that's why people think they did a great job cleaning!). So to be clear, what is noisy are the contacts on the slip ring and fingers. The carbon track (or whatever the material is) is not the source of your noise in normal situations. Now, run even a small current through a perfectly good control and you will definitely have noise. This is true of all controls.

-Chris

 

[Ixnay]

I looked a bit closer at the owners manual, and then the service manual. They can be pretty hard to read sometimes. So far, I see that it is referred to as 'VR301' and I also saw '250K MNX2' . I am not a parts guy so this is as close as I can get. The part number given is RK0971210066. The resistance of this pot is 250k. Can't say if it has a center detent, but that was popular for balance pots.
I agree with the others here in thinking that this may not be a problem with the pot, but elsewhere. FWIW, getting the OEM is likely not possible.