Rebuild a worn out volume control?

[GCATech]

I have an old Sansui receiver/amp that has been good to me for many years. I picked it up used about 1986 and the last few years it has developed an intermittent volume control. Of course, this part is NLA. I took it out and very carefully took it apart, cleaned it up and inspected it under a magnifier. It looks to me that the carbon tracks are almost completely worn off. The ohmmeter shows several dead spots as the shaft is tuned and the operation in circuit bears this out.

Is there anywhere that can redeposit the carbon track? One side is easily accessible but the other is under a crimped shaft that will take some doing to take completely apart and get back together.

The stereo is a Sansui R-30. The part is an Alps #10155700, 150K, BX2 (centertap brought out to a dedicated pin.)

Thanks in advance.

GCATech
(ex Navy ET)

 

[Nigel Goodwin]

Can't help you on rebuilding the pot, I've no idea if anything is available to try and do that or not?.

However, replacing pots with centre taps is a VERY common question here - as such pots are rarely available.

Basically, replace it with a normal stereo pot and ignore the centre tap - the tap is only for loudness compensation, and the better quality amps don't even provide that anyway (as it's just another added distortion).

 

[rjenkinsgb]

Most likely, the centre tap is for a "Loudness" circuit. If you never use that, a conventional pot should work fine.
I've never heard of any place that will rebuild a pot track.

Is it a PCB-mounted part or panel mounted with flying leads? A panel mounted one is far easier to substitute!

Edit.. Snap!

 

[Nigel Goodwin]

I've no idea if it's still available?, and I would imagine probably not, but a number of years ago one of the spares suppliers we used where I use to work were selling 'custom made' pots to order, and also kits for building your own.

Essentially, there were the mechanical parts, and various track values, log, lin and anti-log, and on/off switches.

You simply specified exactly what you wanted (such as four tracks, two log, two anti-log, and a mains on/off switch) and they assembled them for you - or you could order the individual parts and assemble yourself. You could even build/order concentric pots as used in car radios - which was VERY useful, as those were very often unavailable even back then.

I'm doubtful that they are still available?, particularly as volume controls themselves seem pretty hard to find these days, with relatively little choice.

 

[GCATech]

Thanks for all the suggestions. I got lucky and found a used one at a reasonable price on eBay. I can only hope it's not worn like mine. If it is, I found some new units that I might be able to make work. The original part is chassis mounted but is also soldered directly to the circuit board. I think I can just mount the new part upside down and use flying leads to the pcb. I might have to find a different knob because the shaft is shorter than the original. I'm just interested is getting this receiver/amp back to operating condition, not as a collector item. The volume pot is the only issue it has.

I hesitate to ignore the loudness tap. I like the loudness button on the stereo <g>.

 

[Nigel Goodwin]

Thanks for all the suggestions. I got lucky and found a used one at a reasonable price on eBay. I can only hope it's not worn like mine. If it is, I found some new units that I might be able to make work. The original part is chassis mounted but is also soldered directly to the circuit board. I think I can just mount the new part upside down and use flying leads to the pcb.

That's the standard technique, I've done it often over the years - but not for along time now.

I hesitate to ignore the loudness tap. I like the loudness button on the stereo <g>.

If you can find a suitable pot, then no problem.

What I did find when googling, was (expensive) switched attenuator kits, with 128 steps - but they are rather large, and as I said expensive.

Presumably as it's simply a load of switched resistors, you could easily add a tap to each 'track'.

 

[unclejed613]

unless it's a special size/mounting or some other oddball thing, most pots of the same size and mounting style should work fine... somebody likely still makes pots with the loudness tap... look at replacement parts for guitar amplifiers too as i remember there were some that used the loudness tap for something else, usually to do with the tone control filters iirc.