Replacement volume pot for McIntosh C26

[Raccoon1400]

I'm working on a McIntosh C26 and the original volume pot is shot. (resistive contact surface is half gone)
The volume pot has the power switch built in.
There's a reproduction available on ebay but it is very expensive for what it is (and I've used his parts before and they haven't been as balanced as claimed). I'm thinking it would be better to get a decent quality volume pot and just use a power conditioner to switch the entire system.
It doesn't have a loudness tap, so that makes it easier. But it is a 500k pot, and I'm having trouble finding that value.

Any suggestions?

 

[Raccoon1400]

Would it be possible to adapt the circuit to use a lower value pot? Or can I get away with lower without changing anything else?

 

[rayma]

Looks like you can reduce the value of the volume pot just by increasing the value
of the 0.22uF capacitor C20 feeding it. Use a polypropylene type.
The pot mounting hole will not be metric, but the pot will be.
https://www.hifiengine.com/manual_library/mcintosh/c26.shtml
So a 250k volume pot needs 0.47uF, and a 100k volume pot needs 1uF. Voltage rating can be 50V or more.
This does not apply to the loudness control however, which is part of a more complex circuit.

 

[Raccoon1400]

Looks like you can reduce the value of the volume pot just by increasing the value
of the 0.22uF capacitor C20 feeding it. Use a polypropylene type.
The pot mounting hole will not be metric, but the pot will be.
https://www.hifiengine.com/manual_library/mcintosh/c26.shtml
So a 250k volume pot needs 0.47uF, and a 100k volume pot needs 1uF. Voltage rating can be 50V or more.
This does not apply to the loudness control however, which is part of a more complex circuit.

Thanks!
I'd use this, I think. https://www.partsconnexion.com/ALPS-70770.html
I'll need to grind the side of the shaft flat.

 

[wiseoldtech]

Why not just contact McIntosh directly?
They supply replacement parts for older units.
They even have replacement glass fronts for the ones where the black paint flaked off.

 

[Raccoon1400]

Why not just contact McIntosh directly?
They supply replacement parts for older units.
They even have replacement glass fronts for the ones where the black paint flaked off.

Good suggestion. The client did get the new faceplate for the power amp that goes with this.

 

[rayma]

Thanks!
I'd use this, I think. https://www.partsconnexion.com/ALPS-70770.html
I'll need to grind the side of the shaft flat.

The metric shaft is also longer, and a smaller metric diameter, than the original 1/4" dia flat shaft.
If the owner is willing to spring for a new faceplate, just go ahead and buy a NOS pot from McIntosh.
The pot, plus the labor charge for reworking the metric shaft, will end up higher in cost.

 

[wiseoldtech]

The metric shaft is also longer, and a smaller metric diameter, than the original 1/4" dia flat shaft.
If the owner is willing to spring for a new faceplate, just go ahead and buy a NOS pot from McIntosh.
The pot, plus the labor charge for reworking the metric shaft, will end up higher in cost.

Being this is a McIntosh, I don't see a problem with "costs".
Because people insisting on that brand obviously know the possible consequences of parts and repairs.

 

[Raccoon1400]

I still haven't heard back from McIntosh about the pot.

 

[Raccoon1400]

After shipping the McIntosh replacement part would cost almost $200CND

 

[rayma]

Those were custom made for McIntosh, so not surprising they are expensive.

This USED stereo control with switch looks good, it is audio taper but no loudness tap.
https://www.ebay.com/itm/122927818030?hash=item1c9f11a52e:g:eYoAAOSwcj1aKJAJ
This NOS stereo control lwith switch looks good except it is linear, and has no loudness tap.
You could add a 50k resistor between each wiper and ground to law fake a log curve.
That way the stereo tracking should be very good.
https://www.ebay.com/itm/1136845923...cC9Jho18DiviZ8b4uVXhS_wvHdzIy6nhoC_H0QAvD_BwE
Important: if you have to cut off the shaft, clamp the knob end of the shaft in a vise and saw the shaft off
while leaving the pot end free and unclamped. Otherwise the pot could be damaged.

 

[wiseoldtech]

Important: if you have to cut off the shaft, clamp the knob end of the shaft in a vise and saw the shaft off
while leaving the pot end free and unclamped. Otherwise the pot could be damaged.

Yes indeed.... and slipping a protective covering over the shaft, taping it securely, will keep flying metal bits from getting into the bushing and also into the carbon tracks and wiper - which also damage the control.
It's purely common sense and careful planning.

 

[rayma]

Also seal off the pot while sawing to keep out metal filings. I have used a plastic sandwich bag to enclose
the pot, then sealing the opening of the bag to the bushing with masking tape. When finished sawing,
file off the rough edge of the shaft and make sure that it fits into the knob smoothly. then brush all the filings
off of the bag before removing it from the pot. Spray a little deoxit D5 inside, and exercise the control several
times before installation.

 

[Raccoon1400]

I managed to get the Alps pot to fit nicely. I just had to flatten the side of the shaft on bench grinder, and trim the length slightly. I used the advice given in the past few posts to protect the insides of the control. The extra labour to make this part work didn't end up being very much.
The client liked the idea of using a power conditioner to switch everything on and off. This also meant I could upgrade the power cords to polarized ones without making it so he couldn't switch everything on at once, since everything can plug into the power conditioner instead of the preamp.

 

[twerbisk]

Working with old guitar amps, I found a number of parts suppliers catering to that niche market. Older equipment generally had higher resistance values and integrated switches.