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Sansui G-8000 volume potentiometer cracked problem

dapbmw

dapbmw

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E3F0926C-3D33-4AF4-9E14-236353C12666.jpeg E125A03D-1C99-4EC6-A946-8C502FD49529.jpeg 39504CA5-1EC0-4A99-8060-7BD15114F159.jpeg Been restoring this g-8000 for 4 months now. It had the volume cutting out issue and Looked at the f-2800 board and it’s been worked on before as in someone removed the volume lot before, one of the top terminal tabs grey wire connected was loose and it’s broken off from the wafer.

Since this is a carbon type wafer, how can one fix it and still have electrical continuity?

I tried eBay and the usual used parts places online but I cannot find a G-8000 volume potentiometer. This is a dual gang type 150 k ohms. I can find 100k or 200k but not 150k, besides they won’t the top terminal taps for the loudness switch.

Does anyone have a spare for sale?

Is there a workaround this?
 
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Doubtful a good long term repair can be made to that pot even with conductive epoxy to bridge the gap in the carbon track, so replacing it is the only option IMHO. The big G models are seldom parted anymore given their valuation as complete units, so finding an OE pot is a long shot.

My best advice is to look for an Alps black beauty or blue velvet control, not sure they are offered in 150kΩ, but there are models with loudness taps and two gangs. They all have snap in PCB terminals (no ring lugs), so you'd need to solder the wiring to those.

Barring that as a solution, be on the lookout for used post from other makes and models that are the right value and configuration even if the terminals are a different style. Also give Goldpoint level controls (goldpt.com) a look. They are pricey (very high quality rotary switches with precision resistor ladders) but may be the only way to get the value you need.
 
Sansuiman said:
Doubtful a good long term repair can be made to that pot even with conductive epoxy to bridge the gap in the carbon track, so replacing it is the only option IMHO. The big G models are seldom parted anymore given their valuation as complete units, so finding an OE pot is a long shot.

My best advice is to look for an Alps black beauty or blue velvet control, not sure they are offered in 150kΩ, but there are models with loudness taps and two gangs. They all have snap in PCB terminals (no ring lugs), so you'd need to solder the wiring to those.

Barring that as a solution, be on the lookout for used post from other makes and models that are the right value and configuration even if the terminals are a different style. Also give Goldpoint level controls (goldpt.com) a look. They are pricey (very high quality rotary switches with precision resistor ladders) but may be the only way to get the value you need.
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Thanks for the reply Sansuiman! I can only find 100K , 200k and 250k which would work better as a replacement for the dual log 150k's on the g-8000?
 
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150k is a tough one. 100K will not be enough to get zero output with the pot fully counter clockwise, 200K will cut the maximum output from the unit but will work, and 250K would cut the max output even more. Anything you get needs the fourth terminal to support the loudness control or you won't be able to retain that functionality.

The stock pot on the G-8000 also has a detent action (little clicks between steps) and it may not be possible to find a replacement that has that feature, but that would be a small sacrifice to make to get it functional again.

Let me do some digging around and see if I can turn something up.
 
Sansuiman said:
150k is a tough one. 100K will not be enough to get zero output with the pot fully counter clockwise, 200K will cut the maximum output from the unit but will work, and 250K would cut the max output even more. Anything you get needs the fourth terminal to support the loudness control or you won't be able to retain that functionality.

The stock pot on the G-8000 also has a detent action (little clicks between steps) and it may not be possible to find a replacement that has that feature, but that would be a small sacrifice to make to get it functional again.

Let me do some digging around and see if I can turn something up.
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Thank you Sansuiman. I found this on eBay but it is a knurled knob.

https://www.ebay.com/itm/Vintage-Sa...610947?hash=item28944aa203:g:1w4AAOSwih9ewgMA

https://www.ebay.com/itm/Harman-Kar...573235?hash=item2885afa773:g:x3kAAOSwoNldiYJH

this one might work but it maybe hard to swap shafts as that locking ring is next to impossible to open.

https://www.ebay.com/itm/NOS-Alps-v...4&brand=Yamaha&_trksid=p2334524.c100667.m2042
 
The shaft is a minor problem. I've spliced shafts that are too short with some aluminum or brass tubular stock and epoxy, and just cut the shaft off the old pot to use as an extension to get to the correct length and pattern (in this particular case 1/4 round smooth) so the knob can be attached. The key things are the Kohm value and the presence of the loudness tap.

I think that NOS Alps pot in the link is your best bet as it is 150K and has the loudness terminal on it. It is also a good quality part from a known brand and is new, so has no wear to speak of. Just extend the shaft and attach the wiring to the snap tabs. Yes, it's a bit pricey, but it is as close as you are likely to get on short notice.
 
Sansuiman said:
The shaft is a minor problem. I've spliced shafts that are too short with some aluminum or brass tubular stock and epoxy, and just cut the shaft off the old pot to use as an extension to get to the correct length and pattern (in this particular case 1/4 round smooth) so the knob can be attached. The key things are the Kohm value and the presence of the loudness tap.

I think that NOS Alps pot in the link is your best bet as it is 150K and has the loudness terminal on it. It is also a good quality part from a known brand and is new, so has no wear to speak of. Just extend the shaft and attach the wiring to the snap tabs. Yes, it's a bit pricey, but it is as close as you are likely to get on short notice.
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Ok I’ll grab it then and when I get I’ll take into note the tips you wrote here.
 
If you have a small neighborhood hardware store (Ace, True Value or some such) they usuallly have a rack of small metal tube and sheet stock in brass, aluminum and stainless. I've used both brass and aluminum rigid tubing with a 1/4" inside diameter cut long enough to overlap the existing shaft (then epoxied in place with JB Weld or similar) and attached another section of shaft from a donor pot epoxied into the "sleeve", let it set to fully cured and then it is usually good to go. Just make sure the final length is the same as the original pot (measure it first before cutting anything).

Wiring is easy enough, just obseve the correct order of the wires to the terminals. The loudness tap on the new pot is the terminal that starts on top and curves down alongside the wafer as a seperate leg from the three terminals on the phenolic wafer.
 
I think these may be the issue with different value volume controls, as I have had to do this from time to time.

Using 100K instead of 150K will still zero output, because when the pot is fully CCW, the wiper arm should sit at the ground potential on the side of each potentiometer wafer. But you will notice that you get a lot higher volume as you increase to 12 oclock position for example than before because you are halfway to max (50K series resistance) instead of the 75K on the original. You will still get max volume on full CW because the wiper arm of each pot wafer will sit directly on the input to the main amps, without any series resistance inbetween.
Using 200K instead of 150K will still zero output, because when the pot is fully CCW, the wiper arm should sit at the ground potential on the side of each potentiometer wafer. But you will notice that you get a lower volume as you increase to 12 oclock position for example than before because you are halfway to max (100k series resistance) instead of the 75K on the original. You will still get max volume on full CW because the wiper arm of each pot wafer will sit directly on the input to the main amps, without any series resistance inbetween.

I think that the 200k option (if you cant find 150K) is your better option, because you will have more range on the volume, wheras with 100K, you will see the volume increases to a high level very quickly.

The above is my basic explaination. In reality, those pots can be linear pots (Even increases across the entire pot), or logarithmic (not even increases either spread out more on low end, or high end), but I still would see the 200K as the better option.

The fact that the loudness tab is broken will (I believe) only affect the loudness function. If the loudness button isn't pushed, both sides should sound the same.
 
Tom is correct, at maximum CCW the pot should be passing zero signal, and at full CW will be at essentialy zero resistance, so should still pass full signal level. Piss poor off the cuff explanation on my part there. The resposne curve between min and mad will be affected however, probably quite noticeably.

Pete is also correct, patience will often yield the part needed. But how patient is one willing to be when you have a unit on the bench needing to get finished? Sometimes a compromise is made just to get the thing buttoned up and back in service. It's your time and money, so only you can make that call.
 
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