[R-390] re: Call for measurements - 100dB carrier reading

[Bob Camp]

Hi

I suspect that the real answer is a bit more simple.

Low resistance pots once had a reputation as being "low reliability"  
parts. Many places put them on a "do not use" list or made them  
difficult to use (lots of paperwork). Even in the early 1980's this  
was still true at Collins. My guess is that the carrier meter adjust  
was designed to "get around" those regulations.

Bob


On Aug 29, 2007, at 4:16 PM, David Wise wrote:

> Oh, that.  I am convinced that R537 was the
> work of a naive junior engineer, to make a
> 100-ohm pot look like a 15-ohm pot.  (My position
> is weakened, however, by the fact that he used
> 22 not 18.)  And it does - as long as R523 is
> full CW.  I sense a deep wrongness there.
>
> I won't repeat the computations I posted earlier,
> but the upshot is that the smallest value R523 ever
> needs to be set to is about 4 ohms and the largest,
> about 7.  10 is available cheap, but if you could
> find a 3 and put it in series with a 3.9 fixed,
> it would be as good as you can get.
>
> Regards,
> Dave Wise
>
>> -----Original Message-----
>> From: r-390-bounces at mailman.qth.net
>> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of Barry
>> Sent: Wednesday, August 29, 2007 1:01 PM
>> To: R-390 at mailman.qth.net
>> Subject: RE: [R-390] re: Call for measurements - 100dB carrier  
>> reading
>>
>>
>>> One person recommended a 20-ohm pot from
>>> Surplus Sales of Nebraska.  He feels that 18
>>> ohms is the ideal value.  I disagree, 8 is ideal.
>>
>> I was going on the fact that the original 100-ohm pot has a
>> 22-ohm resistor in parallel with it resulting in an 18-ohm
>> variable resistance.
>>
>> Barry - N4BUQ
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