[Boatanchors] More on Carbon Comp V ratings

[Glenn Little WB4UIV]

The OX and OY series appear to be the replacements for carbon comp.
They have similar surge characteristics.
The carbon comps are almost always high in value.
If you bake them, they will come down close to the correct value -- for 
a while, then go high again.

My theory is that the carbon composition resistor is a composite of 
carbon granules and a binding agent, possibly clay.
The molded case makes an imperfect seal to the wire leads.
It is through this imperfect seal that moisture migrates.

The resistance of the resistor is determined by the percentage of carbon 
in the binding agent and how tightly it is compressed.

When moisture swells the binding agent, the carbon granules are less 
tightly packed and the resistance goes up.
The swelling of the binding agent may cause micro cracks in the molded 
case allowing in more moisture.

This is my theory and I am sticking with it until I see a better reason 
for the value shift.

73
Glenn
WB4UIV

On 2/15/2018 10:16 AM, Barry Pfeil wrote:
> Wow, you guys really like to go at it!  Thanks for all the info and
> opinions on my first post.  Getting back to my little Adventurer, FYI the
> parasitic chokes are actually wound on 100 ohm resistors and, since I can't
> measure them in-circuit (DC short) I'll probably replace them just to be
> sure since half the other carbon comps in the rig are way high.  But some
> of the other bad resistors WILL definitely see B-plus, which is 600V in
> this rig, so my question about resistor voltage ratings still stands,
>   David (K6XYZ?) suggested Ohmite OX or OY.  Any other thoughts?
>
> BTW, nice to see those 50 year old 10W wire wounds made by IRC are still
> right on the money in resistance value.
>
> Thanks again ES 73,
> Barry K6RM
> ______________________________________________________________
> Boatanchors mailing list
> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Boatanchors at mailman.qth.net
>
> List Administrator: Gary Harmon, K5JWK
> ** For Assistance: gharmon at idworld.net **
>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

-- 
-----------------------------------------------------------------------
Glenn Little                ARRL Technical Specialist   QCWA  LM 28417
Amateur Callsign:  WB4UIV            wb4uiv at arrl.net    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI LM   NRA LM   SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"