[HBR] Using vintage Carbon Comp resistors

[Hopperdhh at aol.com]

Don and Marvin,

I had heard  that carbon resistors increase in value due to very small 
fractures in the  carbon that propagate.  I can see how this would cause the 
resistance to  increase.  Perhaps moisture in the cracks keep the carbon molecules 
from  touching each other which would make a higher resistance path.  Maybe it 
is  a combination of cracking and moisture.

I do know that even unused carbon  resistors increase in value over time.  
Also, it has been my experience  that high value (100's of K ohms or megohms) 
tend to be the worst offenders --  sometimes being 2 or 3 times their original 
value.

Dan K9WEK  

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