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If black, brown, black, gold was the original color code--well, it's a
pretty strange code for a resistor, starting with black. But sub-10-ohm resistors should have a gold or silver third band, not black, so maybe it didn't change all that much. My suspicion is that it _might_ be a flameproof resistor as you say, but it's quite likely that it's a metal-oxide resistor. The flameproof ones tend to act like fuses (to keep not only themselves but things around them from flaming!), but the metal-oxides have a long reputation of being able to not only melt the solder but burn a hole clear through the board before they give up as resistors. Most of the ones we use have a pale blue case that gets somewhat paler if they've run very hot for a while. I've done some experiments with them, dissipating up to ten watts in a two watt resistor for long periods, and noting that yes, they do change value some, but nothing like a metal or carbon film would. They will survive a long time (hours at least) at five watts with only a few percent value change. Yours could indeed have been orange-orange-black-gold before they got so hot that the paint changed color. I'm curious if you found a schematic or something else to tell you what the design value really was. Cheers, Tom |
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