SV: [AMPS] Stability of Carbon Resistors

[sm5ki]

Here a true story from 1957 when I was repairing the receiver of a Brittish
PYE AM main station in the taxi system of the Swedish town Nynaeshamn. They
complain was, that they no longer could  hear taxis outside the town. Indeed
the measured sensitivity was only some 10 mV or so! Abt 10 composition type
resistors, made by ERIE, had drifted away to some strange value after only
2-3 years of usage!!!

After restoring the original values of resistors with another brand, the
sensitivity went back to the original uV value and normal range was
restored. These white ERIE resitors were used in many Brittish made
electronics and I wonder what problems showed up in other units?

We also remember the very hygroscopic German WIMA condensers that made hell
in many television receivers - but that is another story.

de Hans
----------
>Från: N6BUU@aol.com
>Till: k7fm@teleport.com, amps@contesting.com
>Ämne: Re: [AMPS] Stability of Carbon Resistors
>Datum: tis 7 mar 2000 22.06
>

>
>colin: on the same note, i have a bench ps i built in 1957  lv plus hv plus 
>var. outputs well the xformer went out so in replacing it i checked some of 
>the carbon resistors in the var. voltage circuit.  see below
>
>27 k 2w = 11.86 k
>
>20 k 1w =11.7k
>
>12k 1w =22.7k
>
>330k 1w =535 k
>
>2 parallel 470k 1w =442 k
>
>   a 270 ohm 1w of the same age (1957)  was still 270
>
>   a 470k 1/2 w  was now 496 k
>   
> bear in mind the ps is not on all the time. just now and then for testing 
>and the resistors were run a rated dissp.  or in most cases less.
>
>                                                      regards   hank
>                                                                       
>
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