[R-390] Setting GAIN ADJ

Sat Oct 12 13:48:34 EDT 2024

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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