[volt-nuts] Resistance standard

J. Forster jfor at quik.com
Tue Dec 15 17:46:22 UTC 2009

A good, pure mineral oil is Nujol. Look in the Laxative section.



> Rob Klein wrote:
>>    feedthrough capacitors of low capacitance. After mounting the
>> resistors
>>    and a thorough cleaning, the whole thing will be baked at ~85°C
>>    overnight to get rid of any moisture, then filled with oil and
>> soldered shut.
> I tried something similar to this about 15 years ago.  I needed a 10 KW
> dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed
> the resistors, and connected them together in a series-parallel
> combination to get 50 Ohms.  I measured the value just to make sure.  I
> then got a small drum and filled it with baby oil and put the resistor
> assembly in.  The next day the resistance had changed by more than 50% (
> I don't remember if it increased or decreased.).  The value continued to
> drift and every time the resistor heated up the value changed even
> more.  Tried cleaning, washing in solvent, and baking at high
> temperatures in various combinations but I could never get the value of
> any of the resistors even close to 50 Ohms.  Ended up throwing the whole
> mess away.
> The resistors were uncoated, tubular types so this warning probably does
> not apply to your molded resistors.
> Another post in this topic mentions baby oil.  Even though I had
> problems with my dummy load, it wasn't because of the baby oil.  I also
> tried some lab-grade mineral oil and had the same problem.  I recall
> reading on a mailing list somewhere (probably Time Nuts) that at Los
> Alamos National Lab a group had to buy baby oil because mineral oil was
> considered a hazardous material.
> Brent
> _______________________________________________
> volt-nuts mailing list -- volt-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
> and follow the instructions there.

More information about the volt-nuts mailing list