Fw: [R-390] R-390A trouble (CORRECTION)

Wed, 27 Mar 2002 20:01:23 -0500

Correct the 1st paragraph to read.....

I tapped the tubes when the putt,putt sound is occuring, and when the
antenna trim is detuned, when there is no putt, putt and I hear no harmonics
or any change.

Sorry.

Jim

----- Original Message -----
From: "Jim Temple" <[email protected]>
To: <[email protected]>
Sent: Wednesday, March 27, 2002 7:57 PM
Subject: Re: [R-390] R-390A trouble

> I just checked the tubes on a Hickok 6000A and they test fine,  I also
> swapped in a different set.  No change.  I tapped the tubes when the putt,
> putt sound is occuring, and when the antenna trim is detuned and there is
no
> putt, putt.
>
> I checked the power supply voltages, and I get 260V at F102 and 225V at
> F103.  The 150V regulated is 150.4V.
>
> The sound goes away when V202 1st mixer, V203 2nd mixer, and V204 3rd
mixer
> are individually removed.  I would expect this.  Concerning V202 1st
mixer,
> the sound returns at 8mhz and above, again as expected.  Also, when V201
RF
> Amp is removed, the sound goes away.
>
> All I can surmise is that one or more of the ceramic caps are bad.  I can
> shotgun the caps, but it would be helpful if I started with the most
logical
> stage.  I would pick the V201/6DC6 and go from there.  What do you think?
>
> Jim
>
> ----- Original Message -----
> From: "Barry Hauser" <[email protected]>
> To: "David Wise" <[email protected]>; <[email protected]>
> Sent: Wednesday, March 27, 2002 7:26 PM
> Subject: Re: [R-390] R-390A trouble
>
>
> > The "Yeah, But Dept." chimes in:
> >
> > Yeah, but ... the screeching/motorboating kicks in above the 3 MC band
> only.
> > Doesn't that suggest the RF deck?
> >
> > The Dumb Suggestions Department:
> >
> > Jim - did you test the tubes?  Do the tap test on them?  Even so, some
> tube
> > in the RF deck might not be handling higher freqs.  (or a cap or
something
> > else).  That means swapping out some -- or swapping around.  I'd also
> loosen
> > and retighten likely screws/ground connections.  Sometimes the oxidation
> or
> > residue of MFP varnish can create an unplanned capacitor to ground
rather
> > than ground connection, or maybe even a diode -- or maybe even an LSI
> audio
> > chip with onboard RF chip with programmable screech and motorboat
> sounds. --
> > OK, maybe not that. ;-)
> >
> > Barry
> >
> >
> > ----- Original Message -----
> > From: "David Wise" <[email protected]>
> > To: <[email protected]>
> > Sent: Wednesday, March 27, 2002 6:30 PM
> > Subject: RE: [R-390] R-390A trouble
> >
> >
> > > Sounds to me like regeneration, frequently
> > > caused by a bypass cap letting go or something
> > > losing its ground.  That bad ground you fixed
> > > might not be the only one.
> > >
> > > Divide and conquer.  Got another IF deck?
> > > Swap it in; that's where most of the gain is.
> > >
> > > What do you gentlemen think?
> > >
> > > 73,
> > > Dave Wise
> > >
> > > > -----Original Message-----
> > > > From: Jim Temple [mailto:[email protected]]
> > > >
> > > > OK, I want to fix this receiver.  Here goes.
> > > >
> > > > 1.  R-390A bought as a "massacre" yellow line from Fair Radio.
> > > > 2.  After cleaning, and replacing many of the "problem" caps
> > > > (listed on many
> > > > of the resident web sites), I corrected a below 8mhz problem,
> > > > by finding
> > > > that the ground lug under T-207 was loose and insulated from
> > > > ground by a
> > > > shellac layer.
> > > > 3.  The unit, at first alignment, aligned well.
> > > > 4.  At some point, within a couple of hours of operation, the
receiver
> > > > developed a screeching/motorboat putt putt sound.
> > > _______________________________________________
> > > R-390 mailing list
> > > [email protected]
> > > http://mailman.qth.net/mailman/listinfo/r-390
> > >
> >
> >
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> >
>