Re: Resistor in series


Michael A. Terrell
 

That might be true, for something that is rarely used. If used at least
weekly, it will be fine. If it is a shelf queen, all bets are off.

On Thu, Nov 26, 2020 at 5:00 PM Glenn Little <glennmaillist@bellsouth.net>
wrote:

Baking the resistor will only fix it for the short term.
It will absorb moisture again as you have not fixed the problem, only
the symptom.
There is a crack or 0r other point of moisture incursion in the resistor
case.

The resistor needs to be replaced.

Glenn

On 11/26/2020 6:59 AM, Michael A. Terrell wrote:
Carbon Composition resistors absorb moisture. Bake them for a while
before
tossing them out. Also, high value resistors require voltage across them
to
work at their marked value This used to be plainly marked on reels of CC
resistors. I posted a scan once. I caught hell for 'making up that
bullshit'. They also don't realize the first resistor series was 50%
tolerance. yet they were working on pre-war radios. Once again I was told
that I was 'making up that shit'.

On Thu, Nov 26, 2020 at 12:18 AM Jeff Dutky <jeff.dutky@gmail.com>
wrote:

Tom,

Yes, I had anticipated that these NOS components might not have retained
their specified values. I've been going through my father's effects
while
working on his scopes and finding all sorts of now-50-year-old
components,
some of which were expensive when purchased new, and thinking that some
fair fraction of them are probably now terribly out of spec, if not
completely destroyed (there are a number of big metal can capacitors
that I
know were stored for at least 20 years in a hot attic, and I don't have
much hope that they are still in good condition). I purchased a dozen
resistors in the hope that I could find two that were within spec.

Back in college I worked in receiving QC for a NASA contractor that
built
flight-rated systems. We would first receive a lot of 10 or 20
components
of some description, which we would label and ship over to Goddard. They
would eventually ship us back 2 or 3 components with paint marks and
certification sheets, and we were required to use only those marked
components in the parts we built for them. The other components we had
shipped to them had been tested to destruction, and only the surviving
10%
had been returned to us as flight qualified components. Careful
selection
of parts is something I have thought about ever since.

But what you're saying is that while my intuition was correct, the
actual
math makes a fool of me. I should really just use the metal film
resistors
when they arrive because they are lower noise and the inductance is a
non-issue.

I can always gaze lovingly at the old Allen Bradleys. I'm quite sad that
nobody seems to make resistors that have those nice sharp edges anymore
(or, at least, I haven't found them for sale).

-- Jeff Dutky







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Glenn Little ARRL Technical Specialist QCWA LM 28417
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