A general question. While working late last night, I noticed that as a piece of equipment warmed up, a 470 ohm metal film resistor I had just replaced, began to reduce slightly in value. I was surprised because I thought metal film resistors had a positive temperature coefficient. (And carbon film resistors had a negative temperature coefficient.) So I checked all of the rest of the same type 470 ohm resistors and they too dropped in value as they were heated. However other 470 ohm resistors from a different manufacturer showed a positive temperature coefficient. I then checked several other metal film resistors and they all increased as they were heated. Only two values showed negative and they were both from the same manufacturer in China. They certainly look like typical 1% metal film resistors with 5 color bands. I did notice these 470 ohm resistors didn't drop in value as rapidly as a carbon film resistors would, but it still dropped.
Am I correct in assuming that all metal film resistors increase in value as they heat up?
Am I correct in assuming that all metal film resistors increase in value as they heat up?
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