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Looking for pot !

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 16 May, 2007 » Looking for pot ! « Previous Next »

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davel
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Username: davel

Post Number: 16
Registered: 11-2005


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Posted on Thursday, 10 May, 2007 - 04:26 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi All,
I am looking for a potentometer 6K8 1watt lin with a 1/8 th shaft to repair a chinese bench power supply.not been able to find one yet any suggestions.
Cheers
David
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john_becker
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Username: john_becker

Post Number: 1360
Registered: 05-2005

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Posted on Thursday, 10 May, 2007 - 05:04 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

David, to the best of my knowledge, 6k8 is a non-standard value for pots. The nearest will be 5k (or 4k7) or 10k. Unless someone knows differently ?

J
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davel
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Username: davel

Post Number: 17
Registered: 11-2005


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Posted on Thursday, 10 May, 2007 - 05:36 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks John,
It is currently working using a 5k pot but this has limited the range of the unit .I have tried using fixed resistors but these only move the range up or down.I have throught obout using a 4k7 plus 2k2 but do not have enough panel space.The faulty one is marked WX13-12 6k8 +/- 5%.
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vlf
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Username: vlf

Post Number: 67
Registered: 10-2005

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Posted on Thursday, 10 May, 2007 - 07:23 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi davel...

Use a 10K pot Cermet 1Watt; and place across its 10K resistance a fixed value of 22K, this will bring the total value to 6.875K.

Calculation is: (1?*2?)/(1?+2?)= Answer

thus... (10*22) / (10+22)= 6.875K
.........Times Divide Plus = 6.875K

The above only works using a Scientific Calculator, with (closed brackets), to provide the direct answer result.

Regards, Brian.
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davel
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Username: davel

Post Number: 18
Registered: 11-2005


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Posted on Thursday, 10 May, 2007 - 08:23 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Brian,
Thanks for the info never would have thought of this fix.
Thanks very much
David
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john_becker
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Username: john_becker

Post Number: 1362
Registered: 05-2005

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Posted on Thursday, 10 May, 2007 - 08:38 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Dave, I earlier replied similar to what Brian has said, but my post has gone missing. I agree 22k in parallel with the outer terminals of a 10k pot gives you pretty close to a 6k8 range (R1/R2 where R1 is the pot basic value). Note that comps always have a tolerance value, especialy pots at about 20%.

J
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steerpike
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Username: steerpike

Post Number: 202
Registered: 05-2005


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Posted on Thursday, 10 May, 2007 - 10:03 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Note that parallelling a pot with a fixed resistor 'delinearises' it somewhat, which usually is not too important, but if the panel has markings at various knob positions, these might end up slightly 'out'.

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