[R-390] Mystery Component

[Renee K6FSB]

Barry- 1964 Manual hmmmm  maybe....hmmm..... thanks at least you found 
the possible source. I do not even recall why or what back then....
I wonder since the R390 was being replaced by the R390A no one bothered 
to document it fully?
Renée

On 10/13/24 9:19 PM, Jacques Fortin wrote:
> 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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