Re: Carbon Comp: Aging Causes Out Of Tol?

Yup, carbon composition was notoriously unstable. The phenolic casing was not
hermetic and allowed moisture in and out. About the only way they were better
than carbon film was in power surge rating. A 1 watt could take 5 watts of
overload for a split second without more damage than a small change in value.
Carbon films would flash and flameout.

Also, carbon comps have lower self inductance than carbon film, so you'll
sometimes see them still used in RF power circuits. Sometimes with coils wound
about the body, too.

I remember when Ohmite announced years ago they were ceasing production on their
comps and so many engineers wailed 'No!'. Ohmite relented, but did get to raise
prices.

You may be able to sell them on ebay to people who need replacement parts for
their old gear.


On Sun, 15 May 2005 05:13:49 -0700, "Watson A.Name - \"Watt Sun, the Dark
Remover\"" <NOSPAM@xxxxxxxxxxxxxx> wrote:

>I have fifty 910 ohm 1/4W carbon composition resistors, still in the
>paper tape, which is labeled:
>
>OHMITE
>910 OHM
>1/4 W 5%
>RC07GF911J
>OC9115
>
>Judging from the last line, they're 14 years old. They've never been
>used, AKA New Old Stock. Every resistor measures greater than 5%, some
>are over 1k. Over 14 years, would drift from aging cause them to go
>that far out of tolerance? I have carbon film resistore much older than
>these and they still measure within 5% tolerance, usually within 2%.
>
>Thanks.

.

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