[Premium-Rx] Experiment: How to readjust a drifted carbon comp resistor

[Tisha Hayes]

Usually what causes carbon comp resistors to deteriorate to where the
resistance rises is that the carbon granules gradually suck up moisture.
The heating drives out the moisture so you are seeing the values falling
closer to where they originally were from manufacturing.

Since the lacquer coating on the resistors is going to be deteriorated or
cooked off I would suggest re-sealing the resistor with a lacquer (or clear
fingernail polish) after they have cooled. Notice that the values over the
next few hours and days begin to creep upwards again on the resistors that
were cooked. If you can keep the moisture from re-entering the resistor you
have a better chance of keeping it stable.

Slower, longer duration heat is going to be better than the rapid
treatment. If you had a constant current supply you could estimate the
current draw at the desired resistance and let the resistors run warm. You
want to try to avoid thermal shocks as it is going to embrittle the carbon
granules and make the resistor mechanically fragile (it will crack and
break). Simple wattage calculations (E*I=W) will let you calculate the
thermal wattage.

-- 
Ms. Tisha Hayes. AA4HA

*""In this denial of the right to participate in government, not merely the
degradation of woman and the perpetuation of a great injustice happens, but
the maiming and repudiation of one-half of the moral and intellectual power
of the government of the world." -- Fredrick Douglass"*