[R-390] Setting GAIN ADJ

Sat Oct 12 13:55:31 EDT 2024

Thanks Jacques.  I forgot.

Regards, Larry

On Sat, Oct 12, 2024 at 10:48 AM Jacques Fortin <jacques.f at videotron.ca>
wrote:

> Larry, please remember that Barry is "playing" with a R-390/URR (a non-A
> !).
> So the B+ should be 180V (or very close to: no adjustment for it).
> And yes, the IF deck should be able to deliver -7V to the Diode Load line
> with only 150µV (from a 50 ohms termination of the SG) connected to the
> J525 if the IF.
> See p.75 of the TM11-5820-357-35.
> BTW, I had to change all the B+ feeding resistors in my own IF deck: they
> were all out of range and some measured over 100% of the expected value.
> Do not hope that these 70 years old Allen-Bradley resistors survived...
> For the caps, all those were Sprague Vitamin Q used during manufacturing
> and they should still behave as new, except if some exhibit traces of
> internal oil leakage.
> Those leaking ones HAVE TO be changed.
> No need to test those electrically either: they will SURELY exhibit
> leakage (electrically speaking)..
>
>
> 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 Larry Haney
> Envoyé : 12 octobre 2024 12:26
> À : Barry Scott <72volkswagon at gmail.com>
> Cc : R-390 Mailing List <r-390 at mailman.qth.net>
> Objet : Re: [R-390] Setting GAIN ADJ
>
> 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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