Silver St888 Volume Pot

[floyd]

When you Google 7 pin volume potentiometer there's plenty of result you just have to do some detective work to track down a replacement.

 

[Chester Draus]

Hey all,

Thanks for the feedback, great to see people genuinely interested in helping out. I will attempt the fix the pot first prior to sourcing a replacement

Few things I'd like to clarif:
- recommended adhesive for the wipers?
- recommended contact grease? I do have access to RS contact grease https://au.rs-online.com/mobile/p/contact-cleaners/0503335/

When I get home tonight I'll pin out the pot resistances and upload them.

Again thanks for help, it's really appreciated!

 

[docs]

And if you pinch it ll back together without checking for continuity, good luck pulling it back apart again........ I would put this in caps and bold if it meant it got read but hey, you go for it.

 

[Chester Draus]

Sorry docs, what are referring too?

I'm looking at products now to hold the wipers in place temporarily in case I get it wrong so I can ensure it's correct before I commit

Is there a method you've tried and tested?

 

[docs]

The gluing part is easy, i’ve used a tiny blob of super glue, no problem at all.
But please make sure the actual tracks on the pcb are connected end to end because if a track is broken, you will have to reopen the tabs to repair it.

 

[Chester Draus]

Ah no problem will do - my aim is to bell the tracks out tonight and upload them before proceeding.

Thanks for your advice, dumb question - any specific glue I should look at using?

 

[caution]

- recommended adhesive for the wipers?
- recommended contact grease?

I used JB Weld's Plasticweld epoxy, but any epoxy should work. You should probably avoid cyanoacrylates because they polymerize very quickly and will make a mess of the pot if you goof up and have to start over.
The grease you suggested should work fine

 

[hopey]

Krazy glue generally doesn't work unless you use the plastic primer but go with the epoxys.

 

[caution]

When you Google 7 pin volume potentiometer there's plenty of result you just have to do some detective work to track down a replacement.

If only it were that easy... as far as I know no old stock has ever surfaced. The closest I could find was this one but it needs a hand-crafted retention bracket (see my pics here) and only has 21 volume steps since it's a resistor network, not a carbon track. They're also larger so they may not fit. For those like the Big Ben has, I bought 50k versions of these which may drop right in.

 

[hopey]

When you Google 7 pin volume potentiometer there's plenty of result you just have to do some detective work to track down a replacement.

If only it were that easy... as far as I know no old stock has ever surfaced. The closest I could find was this one but it needs a hand-crafted retention bracket (see my pics here) and only has 21 volume steps since it's a resistor network, not a carbon track. They're also larger so they may not fit. For those like the Big Ben has, I bought 50k versions of these which may drop right in.

Is there a possibility to bypass or bridge the loudness and use a 6pin 50k pot?

 

[caution]

If you bypass it, does increasing the bass/treble at lower volumes still make it sound nice? Can you even crank them far enough to do so? If yes, then this is probably the best way to go, because the loudness circuit isn't even a factor above 40-50% volume.

If it's bridged, you affect the entire volume range. Instead of tapering off as you approach halfway, it's 100% boosting, so you might have to turn down the bass/treble to compensate. Anything over 50% is even worse because now it has a loudness filter when it never did before, and turning down the bass/treble may not be enough, or may not be the right kind of compensation because the loudness circuit boosts different ranges than the bass/treble knobs and breaks differently. Just try it both ways and see which one sounds better for you.

 

[Chester Draus]

Alright so a status report.

Carbon tracks were all good on the pot.

I ended up putting some tails from the pot to the PCB so I could assemble the box and get the wipers on where they needed to go and used some temporary glue strips to hold them in place. (all rivets had snapped flush so it was a little bit of a gamble getting them spot on)

Happy with the location, I glued them in place and lubed the pot - all good! Feels nice, tone and loudness sound like they're working, no scratches, although one issue I have is the location must be just a tiny bit off as the volume doesn't quite cut out, literally just a whimper gets through.

Thanks all for the assist! It's great to have this thing actually working and it sounds fantastic! I do have a lot more work to go;
- one mid / high speaker to replace
- repair the casette player
- replace the lamps
- The bass pot needs work (I found another wiper in the bottom of the case and the bass pot does have issues)
- A clean! It's filthy

I'll start a fresh thread to cover the rebuild. Again, appreciate the help it's great to see people so willing to lend a hand, hopefully I can return the favor one day.

 

[caution]

Since all threads older than a year have been locked, and I don't want to start another thread just about this pot, I'll post it here.

dual 50K Alps pots with a center tap are still available, I totally forgot I bought one a while back. They may take a bit of finagling to fit on some radios, but they are an option.

There are two styles, not entirely sure what the difference is as they are both log (A) 50K pots with a center tap.

http://ebay.com/itm/152296738855

http://ebay.com/itm/254200471496