[R-390] Measuring Resistance Values

[Barry]

Hi Jacques,

I didn’t think it make a difference for resistance readings but was grabbing at straws - especially for the differences I’m seeing. 

Yes, I expect some drift in those carbon comps
but the readings were rather extreme (i. e. 350k vs. 12k).  I could believe 40k or 50k but that was crazy.  Maybe I read 35k as 350k but I can’t be sure now. With the RF deck out, the values are different so I can’t reproduce that at the moment. 

Serial number on the tag is 3044 under contract 14214-PH-51-93. 

Attaching a pic of mine. Yes, the knobs aren’t in their rightful locations but I was just getting some of them where I could test a few things. 

Thanks,
Barry

> On Sep 2, 2024, at 10:52 AM, Jacques Fortin <jacques.f at videotron.ca> wrote:
> 
> Hello Barry,
> A modern DMM with a 10M input can make differences only with the read
> voltages, but not for the resistances values.
> The Allen-Bradley resistors used during your set construction are about 70
> years old now.
> Not surprising that they have raised in value and need to be changed.
> The only good news is that most of the Sprague "Vitamin Q" used within
> should still be good if they show no signs of internal oil leaks.
> 
> BTW, what is the serial and contract number of your set ??
> Mine is a 14214-PH-51-93 sn 2074.
> 
> 73, Jacques, VE2JFE in Montreal
> 
> -----Message d'origine-----
> De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la
> part de Barry
> Envoyé : 2 septembre 2024 10:31
> À : R-390 Mailing List <r-390 at mailman.qth.net>
> Objet : [R-390] Measuring Resistance Values
> 
> Did Collins specify what input impedance a meter should be to properly read
> the resistance values in the manuals?  I did see where a TS-352 was
> mentioned but that's selectable between 20,000 ohms/volt and 1,000
> ohms/volt.
> 
> I started checking the RF Deck in my R-390 and, starting with V201, I noted
> a few values that are significantly high.  I was using a modern DMM with 10M
> input impedance so not sure if that could be the problem but I doubt it
> would account for that much difference but who knows.
> 
> The voltages were off a bit as well but not nearly as much as the resistance
> values.  I suspect the radio will still work with wacky voltages but the R
> values really have me thinking I have work to do.
> 
> Thanks,
> Barry - N4BUQ
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