[Collins] 312B-4

[Glenn Little WB4UIV]

I have a theory about the resistors going high in value. IIRC Carbon 
composition resistors consist of carbon dust and a binder, possibly clay. 
The resistance is determined by the amount of carbon and how tightly it is 
compressed. If we expand the binder with moisture, the carbon dust becomes 
less dense and the resistance goes up. If we heat the resistor and drive 
the water out of the binder, the resistor will again go back to close to 
its original value. How close depended on how the volume of the dried 
resistor compare to the volume of the original resistor. I doubt that you 
can ever get the resistor back down to its original value due to the 
expansion of the casing. This is all my thoughts and based on what I have 
seen. It is not based on any comments from the resistor industry.

Check your early WWII resistors. I find most of these are still within 
tolerance. I wonder what the resistor company did to the sealing of the 
resistors to increase their profits and reduce the reliability of the 
resistor? I have seen S level of reliability resistors that were out of 
tolerance, high, right off the shelf.

This is just my limited observations, however, it seems to hold water.

73
Glenn
WB4UIV

At 10:13 PM 02/21/06, Cam and Juli Hedrick wrote:
>Hi gang,
>I've noticed that my 312B-4 and 312B-5 read output power levels lower by
>about 12% and 20% respectively than my Bird or Drake which give identical
>readings.  I've used two different plugs in the bird and gotten the same
>reading.  What's up...Caps out of value, or maybe carbon resistors?
>By the way, an engineer with IRC has informed me that you can bake a carbon
>resistor and bring it back into tolerance.  Has anyone ever heard such a
>thing before?
>I'll dig deeper, but then again the other meters are working fine.
>Thanks
>Cam
>WA4JKW
>
>
>
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