[Johnson] Old Resistors

[David C. Hallam]

I know it happens, but to triple or quadruple in value?

David
KW4DH

On 4/3/2012 7:53 AM, Jim wrote:
> This is a well documented issue.
> The older carbon resistors tend to drift high in a radio or in the 
> Junke Boxe.
>
> Jim
>
>
>> 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
>
>