BinaryMike
Pelagic EE
I used to buy lots of components from a local military surplus dealer because it was a good way to stock up on high quality parts that would have otherwise been far beyond my budget at the time. I happened to use four 100R 2W(?) wirewound resistors from that old stock recently, and learned a lesson the hard way: There are (rarely) ordinary-looking resistors that are deliberately manufactured with a large temperature coefficient! This example increases its resistance from 100R to about 120R when dissipating 0.6W. I checked six randomly chosen samples out of a bag of 100 or so and confirmed a similar resistance change in every one. I could induce the resistance change with a heat gun just as well as putting current through the samples. And they're definitely wirewound --- I cracked one open to make sure.