Trying to locate a 1 Megohm multiturn pot

[katzcaps]

I'm working on an old Gelman Sciences Power Supply, and the voltage adjust pot is defective.

I cannot seem to find a multiturn 1 Meg pot anywhere...

This is a 10 turn/ 1 Meg pot, 1/4" shaft.

Any ideas?

Thanks!

[Longbow]

Re: Trying to locate a 1 Megohm multiturn pot

These people should be able to help you.
http://www.precisionsales.com/potent...turn/index.htm
Multi-turn pots are always rather pricey, but it depends upon what you are using it for. What are you using it for? Would a more commonly available value work if the circuit layout permitted? The thing to keep in mind is that with large values, the slightest bit of fouling can change the resistance by a lot. Not to mention the liklihood of EMI from the inductive windings and the leads connecting to the pot. Just a few thoughts.

[katzcaps]

Re: Trying to locate a 1 Megohm multiturn pot

Longbow,

I didn't see anything on that site over 100K, unless I'm overlooking it. They seem to have the same stock as State Electronics.

This is on a Gelman Sciences Power Supply - Model 38520. It would be nice to get it functioning again, but it's not worth sinking a huge amount of money into, IMO.

Markings on pot -

VA45R 105A
137-8248

[keeney123]

Re: Trying to locate a 1 Megohm multiturn pot

Same site http://www.precisionsales.com/potent...mil-style.html

Or you could call them up.

[rhomanski]

Re: Trying to locate a 1 Megohm multiturn pot

Does it look something like this? http://www.ebay.com/itm/Calgon-35089...sAAOxyVLNS2afL .

Try here also http://www.oldradioparts.com/potindex.txt .

[katzcaps]

Re: Trying to locate a 1 Megohm multiturn pot

rhomanski,

That does indeed look like the pot. I wonder why do they not list the specs for it in the auction? Would that work for my needs? I don;t know what the numbers mean, since they don't match mine exactly...

[keeney123]

Re: Trying to locate a 1 Megohm multiturn pot

So you might contact these people as they are suppose to carry parts.
http://www.gsisinc.com/posecom/produ...0-Power-Supply

[rhomanski]

Re: Trying to locate a 1 Megohm multiturn pot

They probably don't know the specs and just list the part number. Since it is a different part number, I assume the 105R means 1 Meg, it probably won't work out for you. The 503R probably is 50K or maybe 50Meg. Keep your eyes open though. I'd try the 1 Meg from those other guys too. I got a NOS pot from them, still in the box, for my 1953 radio. The original still barely worked but the new one is well, new.

[katzcaps]

Re: Trying to locate a 1 Megohm multiturn pot

I just came across this item -

I've never used one of these - how do they work? If I understand correctly, I can install one of these on a single turn pot shaft & this thing has a gear reduction giving me 10 turns on a single turn pot? Or am I all wet on this?


http://www.digikey.com/product-detai...002-ND/2408580

[rhomanski]

Re: Trying to locate a 1 Megohm multiturn pot

I think you would have to use it with a 10 turn pot. I don't see any gearing in it, just a number on the side that counts up as you go past zero again. You would need the hole the pot sticks through and a small hole for the pin on the back of it to go through to lock it in position.

[stj]

Re: Trying to locate a 1 Megohm multiturn pot

what's wrong with the old one?

[katzcaps]

Re: Trying to locate a 1 Megohm multiturn pot

I think you would have to use it with a 10 turn pot. I don't see any gearing in it, just a number on the side that counts up as you go past zero again. You would need the hole the pot sticks through and a small hole for the pin on the back of it to go through to lock it in position.

Yeah, I understand that - it would need to have a portion of it "locked" with a pin to keep the whole thing from spinning. I may call them just to verify how it works.

@stj - the old one is worn out. I opened it up & cleaned it, but it is "ate away" at a spot on the carbon track causing a drop when it is rotated to that area.

[keeney123]

Re: Trying to locate a 1 Megohm multiturn pot

They probably don't know the specs and just list the part number. Since it is a different part number, I assume the 105R means 1 Meg, it probably won't work out for you. The 503R probably is 50K or maybe 50Meg. Keep your eyes open though. I'd try the 1 Meg from those other guys too. I got a NOS pot from them, still in the box, for my 1953 radio. The original still barely worked but the new one is well, new.

They say they carry parts for most all manufacturers. They also repair units. So I would think they should know. I believe the MEX in the original part number was for General Instruments. General instruments owned many companies through the years. Some of the companies worked out of NY and were component companies.
I believe that pot is a wire round resistor. You should be able to get a 10 turn linear 1 meg 1/4 or 6.3mm dia. at bourns or most any large resistor manufacturer. You just need to know the wattage.

[stj]

Re: Trying to locate a 1 Megohm multiturn pot

try contacting manufacturers like vishay.