[Johnson] Old Resistors

[David C. Hallam]

Of the three principal types of resistors available, carbon film, metal 
film, and metal oxide, which one exhibits the best long term stability, 
or it more related to the manufacturer?  Given the smaller size of 
today's components, I generally double the wattage rating when I replace 
a resistor.

David
KW4DH

On 4/3/2012 8:31 AM, Carl wrote:
> Thats common with a few brands of resistors. I see 47K screen 
> resistors in Nationals well into the megs fairly often as well as 
> 10X-20X changes in other gear.
>
> OTOH a first run after WW2 NC-240D and a last year 1961 Viking II CDC 
> didnt have a one out of tolerance.
>
> Blame it all on the purchasing departments and managements money 
> saving controls. National changed management shortly after and bought 
> the cheapest they could find. I remember having to replace many even 
> in the mid 60's.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- From: "David C. Hallam" 
> <dhallam at knology.net>
> To: "Johnson List" <johnson at mailman.qth.net>
> Sent: Tuesday, April 03, 2012 7:34 AM
> Subject: [Johnson] Old Resistors
>
>
>> I ran into an interesting situation yesterday.  I was finding multiple
>> spurious signals when I tried to zero beat a received signal with my
>> Invader 2000.  I put it on the bench to find out why.  It turned out to
>> be a carrier oscillator problem.  The unused oscillator was not being
>> turned off so the carrier frequency was a mix of both the 9001.5 and
>> 8998.5 KHz frequencies.  The cause was both of the grid dropping
>> resistors on the 12AU7 oscillator were WAY out of spec and insufficient
>> bias was applied to cut off the unwanted oscillator.
>>
>> The resistors are supposed to be 820K.  One measured 3.2M and the other
>> 4.1M.  Has any seen old resistors go this high in value?  This makes me
>> wonder how many other resistors in this thing have a similar problem.
>>
>> David
>> KW4DH
>>
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>
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