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Old 15th May 2013, 07:35 PM   #1
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Default Wallin Jig 20W non inductive resistor

Hello all
I'm current building a Wallin jig for testing loudspeakers, the Wallin jig needs a 20w non-inductive 8R resistor. Can I use a Caddock power film MP821 resistor for the job? or what is best to use?

Thanks and regards

Stephen
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Old 15th May 2013, 08:17 PM   #2
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The datasheet specifies low inductance.
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Old 1st July 2013, 02:20 AM   #3
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Default winding a non inductive resistor

It is easy too build a non inductive resistor if you are able to calculate the length of a wire from its resistivity and measure its resistance. Once you have the length, cut the wire and find its middle point, bend it to make two parts of equal length and start winding the wire from its center. You can choose any spool, preferably of plastic. In this way you will wind two windings that cancel their magnetic fields each other. If you use copper wire, now you have the trouble of a temperature dependent non inductive resistor. If you use it into an environment where not exist big temperature changes, such dependance is not very bad, but if you are a purist metrologist then you need to use manganine wire.
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Old 1st July 2013, 02:44 AM   #4
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As manganine wire it is not easy to get, constatan wire could be used, since it is also less temperature dependent than copper. Not as good as manganine, but much more available.
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Old 1st July 2013, 08:20 AM   #5
amc184 is offline amc184  New Zealand
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Caddock MP821 looks like a good choice, just remember to put it on a decent heatsink.
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Old 1st July 2013, 01:14 PM   #6
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Quote:
Originally Posted by s_c_leach View Post
the Wallin jig needs a 20w non-inductive 8R resistor
I've used eight 64ohm 2w metal films in parallel.
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