[R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
Barry
n4buq at knology.net
Thu Nov 7 09:40:20 EST 2024
Larry,
Let me also say "thank you" for that document. I've wondered about the various oscillator levels and that document is very informative!
Thanks,
Barry - N4BUQ
> 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
>>
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