[Premium-Rx] wj 205 / A10R14: how to estimate - second try

[Peter Gottlieb]

Over the years I had carefully scavenged carbon comp resistors from equipment.  
Once I started reading them with a good ohmmeter I found that barely any of them 
were still within tolerance and ended up throwing them all out.

When I encounter a stage in an old piece of equipment which won't adjust or is 
mysteriously misbehaving I now replace all the resistors and am sometimes quite 
surprised how far off the old ones are.

Peter



On 7/13/2014 2:03 PM, Peter Ratuschni wrote:
> Hello Boris et al.,
>
> it looks like, that you are in a similar situation with the Regco rcv like me.
>
> # R14 in your case looks like must be 33 ohms-nearest standard value.. colour band's burned, but carbon composition  material inside not.#    (maybe the ge sign caused the text loss?)
>   
> unfortunately it is not that easy. Here is the result of my little experiment:
>   
> I took one of the 47 ohm resistors which I had unsoldered from the receiver (Allen Bradley carbon comp.).
> It`s measured resistance was 60.9 ohms. Connected to a variac, I raised the voltage untill it started slightly to smoke. I turned the voltage down and up again and repeated this for about 3 minutes. After that treatment  it still had its colour rings apparently undamaged and I measured 58.3 ohms. I let it smoke again until only the outer yellow rings were still visible. The colour of the inner rings was burned. After cooling down the 47 ohms resistor measured 26.5 ohms.
>   
> I conclude, that A10R14, which looked even more damaged and was measured with 37 ohms, had it`s nominal value in the range of 47 to 100 ohms.
>   
> It sounds funny, but with some refinements the overload method described above is maybe a possiblity to adjust a upwards drifted carbon comp. resistor back to it`s original value. Of course I would prefer some new 1% resistor but if this is not at hand or if the unit should retain only authentic parts it might be worth a try.
>   
> Btw, I had to be very carefull with the voltage regulator as a first try resulted in a quickly burned resistor which broke in two pieces.
>   
>   
> b.r.
> Peter
>   
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