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Old 17th December 2005, 07:50 AM   #1
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Default Make my own Dual-Concentric pot ??

I need to replace some dual pots, but they are different values, concentricly...10k with 500k.... so that the inner post is one value, and the outer post is another.
If I cannot find these already configured, and I find, say, 10k +10k, and 500k+500k, can I break them apart, and switch the rear pot achieve my needed 10k + 500k ??

I've never opened one up....yet

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Old 17th December 2005, 11:07 AM   #2
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...or would this be the part to hunt down ? :

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Old 17th December 2005, 12:22 PM   #3
dnsey is offline dnsey  United Kingdom
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They're usually very easy to split and reassemble.
Check the shaft sizes though - they don't seem to be as standardised as normal pots.
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Old 18th December 2005, 07:55 AM   #4
AndrewT is online now AndrewT  Scotland
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if you buy from the same maker then the mechanical spec should/could be the same.

It should be easy to swap the wafers and re-assemble the wipers back the way they were.

The big problem may be getting inside without breaking off the little bent lugs that are crimped over. Then rebending them to hold it all in place. Steel fatigues very quickly when bent to 90degrees. This will be a once only dis and re-assembly!!

Alternatively, try to find types that are press fitted together without using those heat deformed pins that effectively rivet them together.

I see some experimentation and scrapping coming along.
Good luck.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 18th December 2005, 08:47 AM   #5
dnsey is offline dnsey  United Kingdom
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Personally, I wouldn't try to change the wafers. D/C pots are usually just complete units 'piggybacked' together, and can be seperated quite easily without further dismantling.
As far as the lugs are concerned, the trick is not to attempt to straighten them out, but to bend them back nearer the pot body, if you see what I mean. They don't need to go very far, and the original crimp isn't compromised and weakened.
Regarding the shaft sizes, I meant that not all will suit the existing knobs - check before buying.
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Old 18th December 2005, 02:06 PM   #6
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First let me tell you what unit I'm Orban 111b spring reverb......and when those pots scratch-and-pop...
it sounds like I'm "dropping rebar in an empty warehouse"
Well, I've been to all the local surplus shops, and surfed the net...but did not find two suitable D/C pots for swapping.
I don't feel real confident swapping the wafers, but maybe I could practice on some old scrap ones first. But I still will need to find the real parts eventually....this is Option #1.

Option 2)..
.... I need (2) D/C 10k/500k ccw log pots. I found (2) 100k/500k linear D/C pots (new old stock/Clarostat). ...but I don't know enough about circuits to know how(or if) it is possible to add resistors to those change the 100k to 10k value....and shunt it, so it acts like a log pot......and.......reverse wire it so it acts like a ccw...?

Option 3)...
Use two seperate pots......instead of trying to find dual concentric.
This means I will have to drill some extra holes in the faceplate...and wire those pots to the board. (I still don't know how to deal with the ccw situation).

Option 4)...
Clean the pots, hope for the best, and/or live with the problem.

...they are located near the Input...and the Output (which is what they and out attenuators).


EDIT :looking closer at the schem, it says cw(clockwise)..not ccw(counterclockwise). The parts list in the manual says "ccw" hmm..
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Old 18th December 2005, 02:12 PM   #7
Nordic is offline Nordic  South Africa
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No way that a dual stepped attenuator, with 2 sets of resistors could do the trick maybe?
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Old 18th December 2005, 04:15 PM   #8
Bobken is offline Bobken  United Kingdom
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Default Noisy pots.

Hi Redrabbit,

I can understand your problems here as I have 'serviced' many similar pots with both carbon and conductive plastic tracks, by varying means over the years, myself.

Making up new units is not too hard if you are reasonably handy and have some suitable tools, but it depends on the construction of the units concerned. If they have clinched-over metal tags holding their bodies together, rather than plastic rivets which are more of a problem to re-construct well, it is possible, as another poster has mentioned. The difficulty here is getting the tags properly tight again, as they tend to spring back (or relax) a bit when being tightened down, so you can end up with a loose fit and later movement between the bodies, which is not good.

Here I have found a small vice is useful, to squeeze the tags down tight on to the bodies, but care is needed not to go too far and crush anything. Also, as already mentioned by others, although I have never broken any of these tags, it is better not to completely straighten the metal tags, but to bend part of the bodies of the pots (very carefully) as you open them up so that what was originally a 90 degree bend, is not straightened out to the full 180 degrees.
They just need to be sprung outwards enough to allow the parts to be separated, and this helps with later re-assembly.

Assuming they are new items, they should stand this careful bending but will probably be less happy being originally bent through 90 degrees in manufacture, then being opening up to a full 180 deg., and then closing them back to the original sharp 90 deg, for a third time. Metal fatigue could cause their breakage.

However, before going to this expense and trouble (and some risk!) I would try using some Caig "CaiLube MCL", available from M. Percy (amongst others) at $12 approx., as this is manufactured expressly for this purpose of restoring noisy pots. Even if it is not entirely successful, it will always be useful as a very good overall contact cleaner for interconnects, binding posts, and mains plugs etc., so your money will not be completely wasted.

It is very rare in my experience, unless the unit is very old or has been abused, that the tracks wear completely through, or that the wiper's fingers will wear right away. A good squirt of this aerosol into the body of the pots (with the unit switched off, of course!) will normally flush out the offending debris and clean up the tracks and fingers etc., especially with a bit of enthusiastic rotating of the pots, but you may need to do this several times. Also, this 'pot cleaner' intentionally leaves a lubricating residue to help with avoiding the problem recurring again.

$12 is admittedly not cheap, but the cost of several new pots needed to make up new units will not be either, and there is always a risk in playing about with these and taking them apart, whereas there is no risk in trying out this 'pot cleaner', and you may not even need to take much apart to try it out.
Incidentally, I have tried numerous other contact cleaners, but nothing else is anything like as successful as this particular product which is designed for this duty, although some temporary success can be achieved with less costly cleaners.

Caig, the manufacturers, are (IMHO) the worlds leader in contact cleaners, and their products are used by aircraft makers, in space-craft applications, telecoms, and hundreds of other critical areas, and it is well worth having a look at their website.

I hope this helps.
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Old 21st December 2005, 01:12 AM   #9
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Thanks everyone.

Bobken, You were right, the Cailube worked. Goes-to-show-ya, try the easiest thing first...something us audio nuts forget.

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