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

Thu Nov 7 03:21:28 EST 2024

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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