[R-390] Popping noise problem

Mon, 28 Jan 2002 12:15:18 +0100

Dear All,
I do agree and I am happy that it is not the cable to the "Diode Load" since
the noise is only present with RF CCW, so with a minimum signal on the
"Diode load". The noise is very low   and it can be heard only with Local
gain completely CW and RF completely CCW. Also, the noise is present even if
a do separate the Limiter circuit from the Diode load.
I tried to change the OA2 , but no success.

I think a need to look more carefully at the suggestion of Mr. Joe Foley,
even if I already tried that procedure..........
the noise source is localized on the "limiter" area...........does anyone
had a problem were the socket of a tube was causing such a problem?

Thanks
Claudio Spiritelli

-----Original Message-----
From: Walter Wilson [mailto:[email protected]]
Sent: Monday, January 28, 2002 12:03 PM
To: Claudio Spiritelli
Cc: [email protected]
Subject: Re: [R-390] Popping noise problem

Claudio,

I suspect James is right on the popping NOT being related to the coax.  The
popping problem I had got worse when the diode load voltage was higher.  It
was especially bad with the BFO in the ON position.  Since yours seems to
occur at what should be low voltages to the Diode Load, I agree with James
that the coax is probably not your problem.

One more item you might check is the OA2 tube on the AF deck.  It can be the
cause of a popping noise when it starts to go bad.  And checking this is
really easy if you have a spare OA2 tube somewhere.

Walter Wilson - KK4DF
http://www.knology.net/~wewilson
(REAL Radios: R-390A(x5), R-390(x2), Viking II, Ranger, Thunderbolt, KWM-2A)

----- Original Message -----
From: "James Miller" <[email protected]>
To: "Claudio Spiritelli" <[email protected]>
Cc: "R-390" <[email protected]>
Sent: Sunday, January 27, 2002 6:30 PM
Subject: Re: [R-390] Popping noise problem

> A follow up...
> On my 390a if I recall correctly the popping would NOT occur as much
> when the RF gain was cranked down.  It seemed to occur more when the RF
> gain was at maximum and there was a strong signal, which meant the diode
> load voltage was at it's highest magnitude...hence the coax insulation
> would tend to break down (causing a pop) when the RF gain was full up
> and a strong signal (AM or carrier) was present.  Claudio mentioned that
> he hears it when the RF gain is turned down (full CCW)...so maybe
> (hopefully) his problem is not coax related.  Just a thought.
>
> Someone emailed me asking for me to discuss the procedure I used... So
> here it is...If it has been determined to be the coax that is bad, you
> can either attempt to thread new ones through the wiring harness or
> leave the bad coax as is in the harness and route the replacements
> separately, perhaps using tie wraps to secure them to the outside of the
> harness.  I chose to remove the old coax and thread replacements through
> the harness.  Believe it or not, I succeeded in doing this while leaving
> the lacing reasonably intact.  The replacement coax should be the very
> small stiff variety with smooth plastic cover (RG-174 I believe).  The
> stiffness and smooth casing helps in threading it through the harness.
> I used the old coax as a "puller."  Cut the old coax from the diode load
> terminals, and solder its braid to the braid of the replacement.  Keep
> the junction as compact and smooth as possible so that it will pass
> through the harness easily.  And you may need to use a lot of silicone
> spray to lubricate the harness and the replacement coax as you thread it
> through.  You will need to loosen or temporarily remove any cable
> clamps, and some, but not all of the lacing and insulating sleeves may
> need to be removed to facilitate movement.   Needle nose pliers, good
> eyesight and a lot of patience pushing and pulling are also needed.
> Alternatively you can remove all lacing, replace the offending coax, and
> then relace the harness with new lacing or tie wraps.  After getting the
> new coaxes into the harness and the ends positioned where they need to
> be, you will need to make the connections.  This is easy at the diode
> load terminal points and the limiter switch at the front panel.  But
> there are connections at the IF module connector that must be done
> also.  You will need to remove the cover from the IF module connector
> and replace the connections there.  In my case, I chose to replace all
> coaxes related  to the IF module connection to the diode load terminals
> and from there to the front panel switch.  My receiver also had the
> diode load test point on the front panel so this had to be accommodated
> as well.  All in all, about  a 2 day job, 2 hours per day for me.  Just
> be sure it's not a bad capacitor etc. first, to avoid this cable repair
> if you can.
>
> Good luck
> Jim N4BE
>
> Claudio Spiritelli wrote:
> >
> > Hello to all,
> >
> > I just discover a problem with my 390A. In order to ear the problem I
must
> > do the following:
> >
> > RF gain .......... completely CCW
> > Local AF gain......completely CW
> > Limiter ...........OFF
> >
> > In this situation there is a "creaking" and "popping" random noise in
the
> > speaker.
> > During normal operation is very hard to ear and only in presence of weak
> > signal.
> >
> > I tried to localize the source of the noise by "sectioning" the
receiver.
> > The AF section does not produce the noise, as well as the RF section.
> > The source appears to be on IF section. I did section more deeply and I
> > removed the "Diode Load" jumper and the noise is still there.
> > This make me to believe that the source is between the "Diode Load
jumper"
> > and the first AF amplifier, witch leaves only the "Limiter".
> > Analyzing the noise with a "scope", I see the noise as a very short but
high
> > spike on the "signal line" in the "limiter" section ( actually when the
> > Diode load jumper is in place, the noise propagate backward to the
detector
> > as well).
> > On the B+ line , I see low frequency variation ( with the scope at is
> > maximum sensibility of 1mV/div) witch I think is the "filtering" trying
to
> > bypass the spikes, so I am assuming that the noise is not coming from
there.
> >
> > When I turn the limiter on, the noise disappear on the audio as well as
I do
> > not see it with the scope and the B+ line does not have any low
frequency
> > variation. That made me to believe that the capacitor C536 was the
cause.
> > Wrong.
> >
> > There are not to many other components in that section that can cause
such a
> > noise and after I replaced the tube ( 5814A), I did run out of options.
> > One more piece of information, it appears that the noise goes away after
the
> > receiver is on for more the 1 hour.
> >
> > Unless my analysis is wrong and the noise has different source, I need
some
> > help from the experts.
> >
> > Thanks for all
> >
> > Claudio Spiritelli
> >
> > _______________________________________________
> > R-390 mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/r-390
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