[R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?

Sat Nov 9 17:13:15 EST 2024

Larry,

Your document prompted me to check the three oscillators in my R390/URR.

On page 46 of TM 11-5820-357-35, the expected voltages of the three
oscillators is defined as being -3v to -11v.  I just checked those and
the 1st oscillator is probably good enough (~ -4.8v) but the 2nd
oscillator and the PTO are both quite under spec.

I had scoped the outputs several months ago and I thought they were
stronger than that (or, at least, good enough) but checking just now
while in STANDBY with the VTVM tells a different story.  Looks like I
have work to do.

Thanks,
Barry - N4BUQ

On Thu, Nov 7, 2024 at 2:21 AM Larry Haney <larry41gm2 at gmail.com> wrote:
>
> Jerry,  Because I found many different 'specs' for the oscillator voltages
> in the A, I wrote a doc about it.  The 390 voltages should be very
> similar to the 390As in my doc: R390A Oscillator Output Level Affects
> <https://www.r-390a.net/R390A%20Oscillator%20Output%20Level%20Affects.pdf>
> .
>
> Regards, Larry
>
> On Wed, Nov 6, 2024 at 2:50 PM <k1jos at att.net> wrote:
>
> > Hi Bob,
> >
> > Thanks, are there any specs as to what a 'normal' range for output would
> > be?   I know working on my KWS-1 recently the mixers took a range from
> > 100mVrms up to 1-2Vrms .
> >
> > Jerry
> >
> > -----Original Message-----
> > From: Bob Camp <kb8tq at n1k.org>
> > Sent: Wednesday, November 6, 2024 5:18 PM
> > To: k1jos at att.net
> > Cc: Larry Haney <larry41gm2 at gmail.com>; r-390 at mailman.qth.net
> > Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
> >
> > Hi
> >
> > The issue isn’t so much a *dead* oscillator as one that is putting out
> > less signal than it should. To get proper mixing, you need a pretty strong
> > signal out of the oscillator.
> >
> > Bob
> >
> > > On Nov 6, 2024, at 4:56 PM, <k1jos at att.net> <k1jos at att.net> wrote:
> > >
> > > Hi Larry,
> > >
> > >
> > >
> > > Would I be able to hear strong stations across the bands if one of the
> > oscillators were not working?
> > >
> > >
> > >
> > > Jerry
> > >
> > >
> > >
> > > From: Larry Haney <larry41gm2 at gmail.com>
> > > Sent: Wednesday, November 6, 2024 3:26 PM
> > > To: k1jos at att.net
> > > Cc: r-390 at mailman.qth.net
> > > Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
> > >
> > >
> > >
> > > Jerry,  Since you will be using a tube extender, you can check the
> > oscillators by scoping the mixer cathodes on the extenders.  You may need
> > to decouple your scope using a 1 M res.
> > >
> > >
> > >
> > > Regards, Larry
> > >
> > >
> > >
> > > On Wed, Nov 6, 2024 at 12:11 PM Larry Haney <larry41gm2 at gmail.com
> > <mailto:larry41gm2 at gmail.com> > wrote:
> > >
> > > Jerry,  Yes, you can do  it with a tube extender.  Use a small coupling
> > capacitor between sig gen and grid of the mixer.  If a mixer oscillator is
> > not functioning, you can simulate it with your sig gen and feed it into the
> > cathode.  It will require a little larger cap for this, maybe around 500
> > pf.  Have fun.
> > >
> > >
> > >
> > > Regards, Larry
> > >
> > >
> > >
> > > On Wed, Nov 6, 2024 at 12:00 PM <k1jos at att.net <mailto:k1jos at att.net> >
> > wrote:
> > >
> > > Hi Larry,
> > >
> > >
> > >
> > > Thanks.  Do I need a set of extension cables to inject into the 3rd
> > mixer or would a tube extender work?  I recently repaired my KWS-1 and
> > thought that was tight, but I didn’t have to disassemble module to test
> > each stage !!
> > >
> > >
> > >
> > > Any practical advice would be appreciated.
> > >
> > >
> > >
> > > Jerry
> > >
> > >
> > >
> > > From: Larry Haney <larry41gm2 at gmail.com <mailto:larry41gm2 at gmail.com>
> > > >
> > > Sent: Wednesday, November 6, 2024 2:00 PM
> > > To: k1jos at att.net <mailto:k1jos at att.net>
> > > Cc: r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net>
> > > Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
> > >
> > >
> > >
> > > Hi Jerry,  For setting the IF gain, you can try a couple things,
> > remember where the gain pot is at right now and then turn it all the way up
> > and see if that improves your problem.  If not, put it back where it was at
> > (it's not critical). Are all the bands about the same deafness?
> > >
> > >
> > >
> > > The input to the 390 & As IF decks is high impedance (about 1 k ohm I
> > think), so the 390A suggests a 50 ohm shunt for use with the 25D sig gen.
> > If you can adjust your sig gen for 1 k ohm, that should work close enough
> > for you to tell if the IF deck is the problem or not.
> > >
> > >
> > >
> > > It sounds like it's the RF deck.  You could work backwards from the
> > > 3rd mixer injecting a signal and see if the required signal input
> > > keeps getting considerably less and less the closer to the antenna you
> > > get.  I'd check the 3rd var IF alignment real closely, you can
> > > manually lift the inductor bar up and see if the signal strength goes
> > > down right away or not.  It should.  One of the small SM coupling caps
> > > may have gone bad
> > >
> > >
> > >
> > > Regards, Larry
> > >
> > >
> > >
> > > On Wed, Nov 6, 2024 at 10:18 AM <k1jos at att.net <mailto:k1jos at att.net> >
> > wrote:
> > >
> > > I have checked all tubes and found two weak 6JB6 in the AF module which
> > I replaced.  The primary issue seems to be inadequate RF gain.
> > >
> > >
> > >
> > > I did a side-by-side comparison of strong and weak stations above and
> > below 8MHz with my HF-380 and R-390.  I found the R-390 was deaf to signals
> > with less than an S-6 reading on the HF-380.  I also compared signal
> > strength to a Flexradio 6700 and the Flex and HF-380 gave similar
> > readings.
> > >
> > >
> > >
> > > Would adjusting the overall Gain (TM-11-856, para. 71 a and b) be a
> > reasonable next step?  If my R-390’s Gain is indeed low, the adjustment
> > requires a signal generator with a Network, Impedance Matching device
> > (CU-406/URM-25F, part of the AN/ URM-25”.  I have a Rigol signal generator
> > where the load impedance can be set to provide correct voltage readout.
> >  Is there any recommended method when not using the AN/URM-25 and impedance
> > matching device?
> > >
> > >
> > >
> > > Jerry
> > >
> > >
> > >
> > >
> > >
> > > From: k1jos at att.net <mailto:k1jos at att.net>  <k1jos at att.net
> > > <mailto:k1jos at att.net> >
> > > Sent: Monday, November 4, 2024 8:14 PM
> > > To: 'r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net> '
> > > <r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net> >
> > > Subject: R-390 (non-A) - Low RF Gain or bad Antenna relay?
> > >
> > >
> > >
> > > Several years ago, Don W5OR (SK) asked me to share administrator
> > > responsibilities with him to manage the r-390 mail list server.  While
> > > I have several R-390/R-390A, I never had the need to repair any.  So,
> > > this is my first post for help…
> > >
> > >
> > >
> > > My R-390 has gone partially deaf.  It sits in a fan-ventilated rack
> > which rarely gets rolled around.  Its last maintenance was in 2002 when Don
> > Heywood did an incredibly thorough job.  It worked great until a few weeks
> > ago when it became completely deaf.  My initial inspection found something
> > bizarre, the RF cable had popped loose (see attached picture)  After
> > reconnecting, it was only partially deaf.  I could tune in moderate and
> > strong signals across all bands but I need to set Local Gain to 7 or higher
> > just about where hum comes into the speakers.  The best description is what
> > you might expect to hear if RF Gain is not at maximum. Also, another ‘clue’
> > is I noticed that switching to CAL does not remove or attenuate a CW or
> > phone signal.. sounds same as if in AGC.  I checked that the antenna relay
> > is working:
> > >
> > >
> > >
> > > *       On powering to STBY – the relay clicks and pulls in visually and
> > checking both twin-ax connector pins, I confirmed both 2 pins are
> > grounded.
> > > *       On switching to AGC or MGC – the relay clicks off and neither of
> > the twin-ax pins are grounded.
> > > *       On switching to CAL – the relay clicks on again and the twinax
> > pins are grounded. The manual says in CAL, unlike in STBY, +180 volts de is
> > applied to the rf. if., af, and calibration oscillator stages and in both
> > STDBY and CAL, terminal 2 of CR801 is grounded to apply 6 volts dc to relay
> > K101.
> > >
> > >
> > >
> > > I also checked Break-In and that works in AGC giving complete silence,
> > but the manual says that’s achieved by grounding the AF output in addition
> > to grounding the antenna inputs.  How does that prevent overloading the RF
> > section with a local transmitter?
> > >
> > >
> > >
> > > My 1st question is, why is there no signal attenuation when switching to
> > CAL?  Is there anything in the electromechanics that could explain this?
> > Is this coincidental to the R-390 partial deafness or part of the same
> > problem?
> > >
> > >
> > >
> > > Pending some replies, my next step is to check the tubes in the RF and
> > audio stages but I’m hoping that my description may sound familiar to the
> > many experienced members of the list.
> > >
> > >
> > >
> > > TIA Jerry
> > >
> > > ______________________________________________________________
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