[R-390] Mystery Component

[Jacques Fortin]

Hi Barry,

I found that this resistor value was logged as 470 ohms in the FIELD DEPOT AND MAINTENANCE PARTS LIST (1964 edition).
But there is no trace of it in any engineering change sheets (the C1, C2, C3 and C4).
R554 is a 2200 ohms in the 1953 parts list, however.
The latest schematics still show R554 as a 2200 ohms part and all the values changes from the C1,2,3,4 are also incorporated in those.
So where is the bug ? In the latest parts list ??
BTW, I have nothing in my notes regarding R554 when I restored my R-390.
Meaning that the R554 fitted in my set when I got it was a 2200 ohms !

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 : 13 octobre 2024 23:43
À : Jacques Fortin <jacques.f at videotron.ca>
Cc : R-390 Mailing List <r-390 at mailman.qth.net>
Objet : Re: [R-390] Mystery Component

Hi Jacques,

One end is connected to R560 and the other end is connected to Z503.  I'm not sure but I think it's R554 and was likely changed from 2.2k to 470 ohms.  Either that, or R554 was mislabeled from the beginning.  I do see where that resistor is still 2.2k for the R-390A/URR so not sure how it ended up being 470 ohms in these radios.

Thanks again,
Barry - N4BUQ


> Hi Barry,
> 
> Eeer... Is that "470 ohms" resistor connected at the same post than 
> the 56K in the picture ??
> Where the other end of it is going ?
> And if your R560 measures 68K, change it !
> It will affect the Carrier Meter calibration and the AGC time constant in "slow"
> mode.
> 
> 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 Scott Envoyé : 13 octobre 2024 23:03 À : Jacques 
> Fortin <jacques.f at videotron.ca> Cc : R-390 Mailing List 
> <r-390 at mailman.qth.net> Objet : Re: [R-390] Mystery Component
> 
> I'd originally started looking at R560.  It's about 68k in mine.  Not 
> really sure how critical that is and I think at most it might have 
> some effect on the AGC time constant.
> 
> I'm pretty sure now, though, that the "mystery" component is a 470 ohm resistor.
> Another list member sent a picture of a couple of his IF modules and 
> one is clearly 470 ohms.  That last band is brown instead of orange.  
> Mine is checking a bit over 500 so probably good enough as-is.  Odd, 
> though, that they used one of the "older" style resistors there.  
> That's what threw me off more than anything.
> 
> Thanks,
> Barry - N4BUQ
> 
> On Sun, Oct 13, 2024 at 8:41 PM Jacques Fortin <jacques.f at videotron.ca> wrote:
>>
>> Barry,
>> That "mystery" component is R553.
>> From your picture, a 1W, 47K ohms, 10% IRC brand resistor (maybe not 
>> the original one, but who knows ??).
>> It connects the 180V supply to the screen grid of V509.
>> R560 (56K ohms) can be seen in the same picture.
>>
>> 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 : 13 octobre 2024 18:15 À : R-390 Mailing 
>> List <r-390 at mailman.qth.net> Objet : [R-390] Mystery Component
>>
>> Maybe not really a “mystery” but I can’t identify the dark brown 
>> cylinder with one yellow and two brown(?) stripes in the AGC 
>> time-constant compartment in my R-490/URR. A 410-ohm resistor?
>>
>> If those are actually violet stripes then I’m even more confused.  Anyone know?
>>
>>
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