[w5ami]

I'm not sure this is the right place to put this, so relocate if it needs to be somehwhere else.

Just a simple question I've wondered about for some time. I have a big box of NOS carbon resistors and wondered how age would effect them. Obviously I can check each one for value, but just curious if anyone knows if age will effect them keeping a value in tolerance after they are put in a circuit with heat, etc. Should I just chunk them?

Brian

[Arran]

If the values are close to what they are marked as then I can't see any harm in using them. It's been my observation that age makes them drift more then use, I have found NOS carbon comp resistors that have drifted in value just sitting in a drawer in a cabinet for 30+ years. This cabinet was stored in a cool, dry, basement before I got it so neither heat nor moisture was the issue in why they drifted.
Regards
Arran

[w5ami]

Good observation Arran. Thanks!

[Mondial]

Yes, I have observed the same thing as Arran. Carbon comps seem to change slowly in value with age, regardless of use. The good thing is as they get older, the rate of change seems to decrease. So your "aged" resistors may actually be more stable than when they were new.

Allen Bradley carbon comps are very reliable despite their age. I very seldom have to change any which have been in use in equipment for decades. I have some which were bought new in the late 70's and although they all seem to drift up a few percent they are still within 5% of their marked value.

Other brands do not seem to fare as well. TRW/IRC and Stackpole come to mind as being very unreliable.

[Arran]

I had some carbon composition resistors that were so far off I simply tossed them, I suppose I could have relabeled them but it just not worth the effort given how cheap new ones are. The worst ones I've found, other then the body end dot kind, are the types with a light brown and roughly finished phenolic shell, I'm not certain but I think that they may have been surplus from the late 1940s or 50s.
Regards
Arran

[w5ami]

Sounds like IRC resistors Arran. I've encountered many of them in late 40 and 50's ham receivers. Rough texture to the body, and nearly always way off. The AB's I've seens are nearly always good.

[w5ami]

"Aged Resistors". Well, good point Mondial. Especially if they started life as being a little low since most I've seen usually increase in resistance. I do see some IRC's in that box, so bet they are bad, but I will check them anyway. Maybe I will have a lot of keepers though. I think I will still just use these in a pinch since like like Arran said, they are cheap enough to buy new. It is getting where many places require a minimum order, and/or charge a lot to ship just a few. Thanks for the idea fellows!

[Raleigh]

I have a friend who collects and restores old calculators from the '70s. He noticed that resistors deteriorate when not used, but can be preserved or restored by periodic use. He uses calculators in his work, so his practice has been to take to work and use a different calculator from his collection each week. He says they last a lot better with periodic use.