[R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
k1jos at att.net
k1jos at att.net
Thu Nov 7 08:29:37 EST 2024
Hi Larry,
This is perfect… just what I was asking about. Many thanks.
Do you think 10Meg is high enough impedance as with a modern DMM? Alternately, I like using a modern digital scope with 10x probe would work as well. I used it for my KWS-1 repairs and found the RF Vrms or Vp-p voltage calculations to be pretty accurate, certainly in the range of a few tenths of a volt.
Best,
Jerry
From: Larry Haney <larry41gm2 at gmail.com>
Sent: Thursday, November 7, 2024 3:21 AM
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, 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 <mailto: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 <mailto:kb8tq at n1k.org> >
Sent: Wednesday, November 6, 2024 5:18 PM
To: k1jos at att.net <mailto:k1jos at att.net>
Cc: Larry Haney <larry41gm2 at gmail.com <mailto:larry41gm2 at gmail.com> >; 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
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 <mailto:k1jos at att.net> > <k1jos at att.net <mailto: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 <mailto:larry41gm2 at gmail.com> >
> Sent: Wednesday, November 6, 2024 3:26 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?
>
>
>
> 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> <mailto: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> <mailto: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> <mailto: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> <mailto:k1jos at att.net <mailto:k1jos at att.net> >
> Cc: r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net> <mailto: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> <mailto: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> <mailto:k1jos at att.net <mailto:k1jos at att.net> > <k1jos at att.net <mailto:k1jos at att.net>
> <mailto: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> <mailto: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> <mailto: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
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net <mailto:R-390 at mailman.qth.net> <mailto:R-390 at mailman.qth.net <mailto:R-390 at mailman.qth.net> >
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net <mailto:R-390 at mailman.qth.net>
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html
More information about the R-390
mailing list