[Johnson] Old Resistors

[Patrick Thrush]

This is right on target with what I am finding whilst rebuilding a National
NC-300.

Although this is the 'Johnson' group, many here have junk boxes.  I am
looking for a part for the aforementioned NC-300.  It's billed as an
"Antenna Transformer: 80 Meter band", and has a National part number of
B15295.  Each band has one of these as input to the RF amp off a rotary
switch.  The RF amp in this one seems to have had a bad experience.  A
hambone tube substitution was made and it seems every resistor possible in
that circuit was gradually cooked out.  Including the little wound input
coil I need--which is nicely toasted.

Anyone have one, or a lead on where one might be found?

PT



73,
 
Patrick Thrush, AE1PT
Bath, NY  14810
http://www.ae1pt.com
42.333  -77.309   CQZ 5  FN12ih
SKCC #4473


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
>>
>> --
>> There are four boxes to use in defense of Liberty:
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>> VOTE for REAL CHANGE in 2012.
>>
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