[ARC5] Carbon Comp Drift

[Dennis Monticelli]

It's the binder, guys.  Temp cycling (even unpowered) will alter the
built-in mechanical stress.  I would not be surprised to learn that the
binder loses it's binding strength over long periods of time even without
the acceleration of temp cycling.  As the binder weakens the particles are
not mushed as tightly together and thus the resistance drifts upward.

*"Fifty years ago, carbon composition resistors were widely used in
consumer electronics. Because of the low stability of the resistance value,
this type of resistor is not suitable for any modern high precision
application. For example, the resistance value can change up to 5% over a
shelf life of one year.  With heavy use the value changes even more: up to
15% for a 2000h test at full rating with 70°C. Soldering can cause a 2%
change. The reason for this instability is inherent to the design of the
resistor. The carbon composition contains materials with different heat
expansion properties. When the conducting carbon particles and the
nonconducting binder heat up or cool down, stresses arise in the resistor
body. The mechanical contact between the conducting particles will change,
and this leads to a change in resistance value."*

Read more http://www.resistorguide.com/carbon-composition-resistor/

Dennis AE6C

On Fri, Mar 1, 2019 at 4:49 PM Robert Eleazer <releazer at earthlink.net>
wrote:

> I never suspected that resistors could change value without first being
> overloaded with current, but around 1982 I bought a TS-34 scope at a ham
> swap meet for $1.00 and found that it worked - but would not focus.  I
> found that all of the 2W resistors, all high resistance value units, had
> just about opened up.  I walked down to the local Layfayette store and
> bought some replacements; installing them instead of the originals fixed
> the scope.
>
> I inherited a large number of carbon comp resistors from a friend some
> years back.  I found that many of them now exceed their original tolerances
> on the high side.  In the GRC-9 I found a 230 ohm that went to something
> like 550 ohm, a 33K that went to 45K, but also a 27K that is still at about
> 27.5K
>
> I am tempted to ask if there is a vanish or coating that would arrest this
> process, but the GRC-9 was MFPed in 1950 and that did not help it.
>
> Wayne
> WB5WSV
>
>
>
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> Virus-free.
> www.avg.com
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
> <#m_-7910156547813297006_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: https://www.qsl.net/donate.html
> Message delivered to dennis.monticelli at gmail.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20190301/3efcd09e/attachment.html>