Repairing a GR-510 unit.

[GEOelectronics]

This is a recent "New" eBay purchase,

It's a GR-510 decade resistor and obviously it's not new.

The repair was informative however and I'll take many more measurements and better pictures before writing it up a a .PDF

Meantime ere are the raw pictures in sequence:
http://www.qsl.net/k/k0ff/Metrology/GR-510_Repair/

Here's my question- how can the salvaged wire be soldered? It seems to be something akin to Nichrome ad resists all my efforts to solder.

George Dowell

[Conrad Hoffman]

The wire was soldered before. It's probably manganin or constantan. Sand it and use flux to solder it. If the salvaged wire is from the burned section, it's been way overheated and I'd salvage it right to the trash can. That's a perfectly good repair, though I try to rewind sections with new resistance wire where possible, just to preserve the look.

[GEOelectronics]

Thanks for your reply Conrad.
One of the reasons I salvaged the wire is to analyze its elemental content , physical dimensions, hardness, resistance per unit of measurement etc. That's a big part of my metrology hobby. My elemental analysis is limited to those heavier than scandium at the moment, but trying o lower that bar o a shoestring budget takes time.

Yes it was soldered before but how was it prepped? Maybe a acid etch? Special flux?

My efforts with 700 F temperatures ad ordinary electronic flux didn't work well at all.
By the way, the heater........errrr.......I mean resistance wires are soldered to the main wires with soft solder, but at the other ed where those main wires attach to the massive copper switch contacts, the solder is very much harder variety. Will eventually check that solder for possible silver content.

The resistance per foot was rather high , only measured a less than 1/2" segment - it was 3 Ohms already.

[Vgkid]

Depending on age the 510 decades used manganin or evanohm. Since yours has all silver contacts it is going to be evanohm.

[Conrad Hoffman]

Evanohm is a lot like nichrome and can't be soldered. It was probably silver brazed or spot welded to something more solderable. Constantan actually makes a decent resistor, save for the horrible thermal emf against copper- thus you'll find it mostly for thermocouples. I still like manganin because of the solderabilty.

How are you measuring alloy content? I'd love to be able to do that.

[GEOelectronics]

"How do you analyze alloy content?"
 Well I developed ( I hate to overuse he word "invented" the Home Lab  analyzer.
It can analyzed stable elements as well as radioactive ones. I

[Conrad Hoffman]

Wow, that's absolutely fantastic. I also like your writing style. Too deep a rabbit hole for me right now, but it's tempting. In another life I helped design scanning tunneling microscopes. Though they seem difficult, it's another one of those things that isn't too hard to do at home, if you have a bit of electronic ability and some mechanical fabrication ability.

[GEOelectronics]

Fine on the advanced microscopes.

George Dowell