[R-390] Resistor Tolerances

Mon, 29 Jul 2002 22:16:24 -0700

I wouldn't expect you to bake them.  While it's not "real world" in a test
bench environment, I promise you it is "real world" during equipment
manufacturer's incoming inspections and during military audits of component
vendors.

I only wanted to be sure you knew the measured value could be significantly
shifted by moisture absorption.  This would have been understood and
accounted for during the design.  As a result, a 5% or 10% rated carbon
composition resistor with a measured value in the +- 20% range shouldn't
necessarily be considered a component requiring replacement.

- greg

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of scott
Sent: Monday, July 29, 2002 4:45 AM
To: [email protected]
Subject: Re: [R-390] Resistor Tolerances

Well I never buy NOS resistors and certainly not caps.  Baking resistors
before measuring
tolerance is just not the real world, even though most boat anchors do just
that.  :-)
The real question I have is: If the tolerance needs to be held to original
specs on any specific
areas of this set.  I am trying to rely on someone's experience to save me a
lot of
needless work now or in the future.  Most of the TV and radio restoration
work I have
done, +15% is OK, even on a 10% spec resistor,  and I have not had
performance problems as a result.
Of course if a 5% is specifically called for, I will hold it to tighter
tolerances.  Most, if not all, of the resistors seem
to be 10% in my modules and I am thinking that this was just a military
requirement rather than
an necessity.

Thank You,
Scott

----- Original Message -----
From: "JAMES T BRANNIGAN" <[email protected]>
To: "Greg Werstiuk" <[email protected]>; "scott"
<[email protected]>; <[email protected]>
Sent: Monday, July 29, 2002 7:22 AM
Subject: Re: [R-390] Resistor Tolerances

> There was an article in QST several months ago that was a real
"eye-opener"
> about stored resistors.
>
> Jim
>
>
> > Scott -
> >
> > I assume the resistors used in R-390x's are carbon composition.
Moisture
> > absorption alone will shift their tolerance up to about +-20%.
> >
> > When they were more commonly used (20 years ago), I occasionally had to
> > educate customer incoming inspection departments claiming to have
received
> > "out of tolerance" product with the proper method for measuring the
> > resistance value of carbon composition resistors.
> >
> > Among other requirements, before measuring resistance, they must be
baked
> > for a specific period of time at a specific temperature to eliminate
> > absorbed moisture.
> >
> > - Greg
>
>
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