[R-390] Setting GAIN ADJ

[Barry Scott]

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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