Electronics > Metrology

soldering eureka wire

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m3vuv:
Hi all,ive an old avometer model8 mk1,It has a wrecked bottom resistance board,one resistor is wirewound with 120 turns of eureka wire approx 980 ohms,this needs replacing,i have the wire,its silk covered but any idea how to solder this as its 44swg,cant see how to remove the silk to solder it without destroying the wire,can anyone tell me the best way to do it?,tia.

jpanhalt:
For very fine wire, I use a molten salt bath.  NaOH or KOH (or a mixture) melts at a fairly low temp.  Adding a little NaNO3 can help.  My bath is just a steel block with a hole for the lye and a second hole for a thermometer/thermocouple.

I did some studies of various mixtures (portion of Table attached) years ago.  Silk is basically a protein and should come off very easily compared to the non-solderable magnet wire enamel that I studied.  If you are careful, you can avoid the darkening.  In any event, what comes out is solderable with typical Kester 44 flux.

You can also try a soft flame.

RandallMcRee:

--- Quote from: m3vuv on January 01, 2022, 02:00:01 pm ---Hi all,ive an old avometer model8 mk1,It has a wrecked bottom resistance board,one resistor is wirewound with 120 turns of eureka wire approx 980 ohms,this needs replacing,i have the wire,its silk covered but any idea how to solder this as its 44swg,cant see how to remove the silk to solder it without destroying the wire,can anyone tell me the best way to do it?,tia.

--- End quote ---

What is "eureka wire"?

Why not simply replace the resistor with an equivalent, modern, WW or metal foil?

(Do we need a test equipment for masochists subsection in eevblog??)

jpanhalt:
At first, I thought maybe it was such fine gauge wire that when you soldered it, you yelled, "eureka."  Then, I looked it up: https://en.wikipedia.org/wiki/Constantan  ;)

Vtile:
Does the blob of solder at the tip of iron trick work with silk as it works with coil/enamel wire. So the technique is to melt a blob of solder to hot 300+deg.C iron and then poke the wire through the blob, so the exposed end will take the solder and with help of heat kind of burn and wrap the coating away.

I assume that you have proper bakelite resistance bridge to verify the resistance (and not these digital nonsence with excessive display numbers), plus a bunsen burner heated soldering iron!  :box:

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