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

Wed Nov 6 15:11:10 EST 2024

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> 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>
> *Sent:* Wednesday, November 6, 2024 2:00 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?
>
>
>
> 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> 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 <k1jos at att.net>
> Sent: Monday, November 4, 2024 8:14 PM
> To: 'r-390 at mailman.qth.net' <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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