[R-390] Setting GAIN ADJ

[Larry Haney]

Hi Barry,  The gain in your IF is too low.  Is it the same in each of the
upper 4 bandwidths?  Have you swapped V501 through V504 and V506?  Is the
B+ about 200 vdc?  Have you checked all the cathode and screen bypass
caps?  And all the plate B+ dropping resistors (2200 ohms)?

Regards, Larry

On Sat, Oct 12, 2024 at 8:48 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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