Can't get solder to stick

[HipoFutura]

I'm working with a 50 or so year old transformer with cloth leads. On of the leads will not fuse with the solder. I'm using 60/40 solder. I've tried several times and have used rosin paste flux. What's the trick to get this to work? There must be some sort of contamination on the lead.

Don

[SY]

Try scraping it clean with a sharp blade. Sometimes terminals get some sort of surface contamination that is really, really difficult to remove; I've just had to throw out some otherwise nice tube sockets because of that. With a wire, you might have a chance if the base metal is copper.

If all else fails, you could do a bit of surgery and replace that recalcitrant lead.

[auplater]

Originally posted by HipoFutura
I'm working with a 50 or so year old transformer with cloth leads. On of the leads will not fuse with the solder. I'm using 60/40 solder. I've tried several times and have used rosin paste flux. What's the trick to get this to work? There must be some sort of contamination on the lead.

Don

If scraping doesn't work, try using flux with chloride in it (plumbers flux). Often recalcitant oxides can react with organic fluxes forming a tough burned on glop that's hard to remove. I've used scotchbrite and/or sandpaper to expose "virgin" metal on these older leads. If it stays silvery (not copper) you've got some other wire type that needs an aggresive flux.

hope this helps...

auplater

[Cal Weldon]

sometimes steel wool works well.

[HipoFutura]

Well, I got it. I seperated the strands and scraped each with a razor. Once I had bright copper I applied the rosin and solder. It worked. This is a time consuming process. I'm glad only one of the eleven leads had a problem. Thanks guys!

Don

[lndm]

Good to hear you worked it out.

Some thoughts. Naturally, you want to be careful with copper as it is easy to break. If you lay the stranded wire on a hard surface and scrape it with an angled blade like spreading butter on toast, you'll expose enough bare copper to begin the bonding process. Now the iron will be able to heat the copper and the contamination may break down more readily.

[rcavictim]

Originally posted by SY
Sometimes terminals get some sort of surface contamination that is really, really difficult to remove; I've just had to throw out some otherwise nice tube sockets because of that.

Sy, All,

I bought a pile of NOS bakelite octal sockets that refuse to wet with solder. By painting the terminals with dilute muriatic acid and a paint brush the oxide layer disappeared quickly and completely. The acid needs to be washed out with a session under the tap however as it will make a conductive film, variably worse with humidity out of the bakelite between terminals if not washed away.

[Eusebius]

Are there any other acids that work on bad socket contacts? Anything common like vinegar or lemon juice? Where do you get muriatic acid?

I've been threading solid core wire through the contacts and twisting it so it's tight, then soldering to the new wire. Desperate measures!!

[AudioFreak]

Originally posted by Eusebius
muriatic acid?

Otherwise known as Hydrochloric Acid.

[rpapps]

Also known as spirits of salts.
You should be able to find it at a hardware or builders supply store. It's used for cleaning cement off brickwork and etching cement prior to painting.
Cheers
Rob