[R-390] Setting GAIN ADJ

[Barry]

Monday morning... :(

"J252" should have been J525 in that first paragraph.  Apologies.

Barry - N4BUQ

> Over the weekend, I discovered that I had been plugging in the signal
> generator to the wrong jack in the IF deck.  I had been mistakenly
> using J526 but the instructions clearly state to use J525 and using
> J252 makes a considerable difference in the ability to get -7v with
> 150uv input.  I don't know how I got it in my head that J526 was the
> right one to use!
> 
> In light of the discussion of the resonance of the crystal filter, I'm
> now wondering if that's having more of a negative influence on gain in
> my IF deck and a proper alignment using that resonant frequency will
> reduce/eliminate the difference between the two jacks.  Regardless, if
> the manual states to use J525, then I should use it for this setting.
> 
> Thanks,
> Barry - N4BUQ
> 
> On Sat, Oct 12, 2024 at 10:48 AM Barry Scott <72volkswagon at gmail.com> wrote:
>>
>> I can get greater than -7v without a 50-ohm terminator but not with
>> it.  From what I can measure with an HP-410C, the HP-8640B needs the
>> terminator to accurately reflect the voltage on its meter and,
>> therefore, I should be using the terminator for this.
>>
>> Of course, I could most likely get that output with, perhaps, 225uv
>> and I may try that just to see how I like it.
>>
>> I need to do some voltage and resistance checks in the IF deck.  I
>> haven't done that yet and I suspect there are some drifted resistors.
>> If not that, then I could have some weak tubes.  I'll know more once I
>> run some checks.
>>
>> Thanks,
>> Barry - N4BUQ
>> Thanks,
>> Barry - N4BUQ
>>
>> On Fri, Oct 11, 2024 at 10:52 PM Larry Haney <larry41gm2 at gmail.com> wrote:
>> >
>> > Hi Barry,  If your 390 is in correct working order then Chuck's short cut is
>> > good to use.  But if you are not positive that it is working correctly, then
>> > use the '55 tech ref method you ref'd.  And, the IF input is not low impedance,
>> > so the sig gen output will need to have a 50 ohm load on it and the gain adjust
>> > must not be at the ends of its adjustment.
>> >
>> > Regards, Larry
>> >
>> > On Fri, Oct 11, 2024 at 7:49 PM Barry Scott <72volkswagon at gmail.com> wrote:
>> >>
>> >> Yes, that's the 1955 version that I was referring to where it
>> >> describes using the IF input and a 30% modulated 455kc signal at 150uV
>> >> to produce -7.0V at the Diode Load.  The later paper manual I have
>> >> from 1962 uses the antenna input for this.  Chuck Rippel's method uses
>> >> strictly the noise level and the LINE GAIN meter to set it.  I'm a bit
>> >> confused as to what's the best way.
>> >>
>> >> Thanks,
>> >> Barry - N4BUQ
>> >>
>> >> On Fri, Oct 11, 2024 at 8:56 PM Jim Whartenby via R-390
>> >> <r-390 at mailman.qth.net> wrote:
>> >> >
>> >> > https://bama.edebris.com/download/military/r390/Collins_R390_1953.pdf
>> >> >
>> >> > Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy
>> >> >
>> >> >     On Friday, October 11, 2024 at 06:16:31 PM CDT, Barry Scott
>> >> >     <72volkswagon at gmail.com> wrote:
>> >> >
>> >> >  Looking at the older (1955) vs newer (1962) manuals for the R-390/URR,
>> >> > the older one describes setting the GAIN ADJ pot using input directly
>> >> > into the IF deck; whereas the newer one describes setting it using the
>> >> > antenna input jack.  Is one method any better or preferred to the
>> >> > other?
>> >> >
>> >> > One of the reasons I'm asking is that when I try the direct input to
>> >> > the IF deck method, I can't get -0,7V on the Diode Load which makes me
>> >> > think I have a gain problem in the IF deck.
>> >> >
>> >> > I know there were several posts about this over the years but I've
>> >> > lost track of those for the most part so I thought I'd ask.
>> >> >
>> >> > Thanks,
>> >> > Barry - N4BUQ
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