[R-390] New owner with (probably dumb) questions

[David Wise]

Just to clarify the expected behavior of Dial Lock,
Zero, Antenna Trim, and the carrier meter:

1. The Dial Lock mechanism squeezes a clamp against
a disc attached to the KC knob.  As you turn Dial
Lock clockwise, it will become harder and harder to
turn.  At the same time, the KC knob will also become
harder to turn, quickly getting to a point where reasonable
force will not turn it at all.  As the knob is rotated
clockwise, the shaft it's on screws itself into the panel,
and at some point the skirt will hang up against the
retaining nut.  While painstaking adjustment will
get it to hang up at exactly the point you should stop
turning, I don't think it was Collins' intent that anyone
bother.  You simply "know" how tight to turn it.
If the knob abruptly stops turning with the KC knob
still free, the mechanism is either out of adjustment
or broken.

2. The Zero mechanism disengages a clutch in the frequency
readout.  Like Dial Lock, it gets harder and harder
to turn as it's tightened down and will eventually
hang up.  Sometime before it's unreasonably tight,
motion of the KC knob should no longer cause the
frequency display to change.  At this point, the KC
knob is still tuning the radio as before, but the
readout is disengaged.  If you started with the
readout on a 100KC boundary, you can line up the radio
with the calibrator's 100KC marker.  Because each band
is controlled by a different crystal*, you may have to
do this every time you switch bands.

* With some exceptions; it's too technical for this post.

3. The antenna trim control goes around and around;
there's no end stop.  At the factory they put a dab
of paint on the shaft to help you replace the knob
after removing it.

4. The design of the carrier meter circuit is such that
it does not display a "fake" high reading when the RF GAIN
control is retarded.  This is not due to any magical
balance of opposing currents.  The tubes that drive the
meter are simply not under control of the RF GAIN pot.
If there is no signal input, the meter should be 0
regardless of RF GAIN.  If there is signal, the meter
will go down as RF GAIN is retarded.

Even without signal, you may see a shift in the carrier
meter when you switch between MGC and AGC.  This is because
the AGC line is clamped to ground by a pair of fairly
poor diodes, namely, the suppressor grids of two of the
IF amps.  Working against this is a weak pullup to B+.
The result may be anything from ground to a volt or so
positive.  On the other hand, MGC grounds the line
hard.  Adding a 1N914 would minimize this effect.

Finally, you may get a carrier reading in MGC mode on
very strong signals.  This signifies 4th IF overload and
is a deliberate characteristic of the meter circuit design.

73,
Dave Wise

> -----Original Message-----
> From: Darryl Jones [mailto:sherri-darryl@erols.com]
> Sent: Sunday, April 20, 2003 10:16 AM
> To: mikea; R-390 List
> Subject: Re: [R-390] New owner with (probably dumb) questions
>=20
>=20
> Hi Mike,
>=20
> > If your new rig has an Antenna Trim control, then it's not=20
> an R-390A,
> > but the less common and (IMHO, anyway) more desirable R-390=20
> -- unless
> > you have a variant I never heard of. WHat does the=20
> nomenclature plate
> > say, _exactly_?
>=20
> R-390A/URR Serial #212 Stewart-Warner Electronics, Order # 20139-PC-60
> The Ant Trim is directly abobe the plate.
>=20
> > Antenna Trim on mine does have unlimited travel, but the Dial Lock
> > does _not_: yours should stop after a reasonable number of turns
> > clockwise.
>=20
> I turned it 360 degrees three times and it locked in place,=20
> so all seems
> well. Thank you :)
>=20
> > It pushes in on a clutch that disengages the frequency
> > indicator from the tuning mechanism, so that one can set the numbers
> > to some multiple of 100 KHz, then turn the Zero Adjuster to=20
> disengage
> > the clutch and set the electronics to that frequency without moving
> > the numbers from where they're set.
> >
> > Dial Lock is just a mechanical clamp that closes on a disc=20
> attached to
> > the main (Kilocycles) tuning shaft; it's in two parts, plus a shaft
> > attached to the Dial Lock knob, and it may be that the=20
> moving part of
> > the clamp is missing or mispositioned.
>=20
> It seemed loose in the case, so I tightened it, and now it=20
> takes only one
> turn from stop to stop.
>=20
> > > I changed the power cord to 3 wire as per mil spec, and=20
> fired it up, but
> > > some
> > > of the tubes that tested as "good" (upper 60's) seemed to=20
> balk and I
> don't
> > > have any audio at all, and the Carrier Level meter is=20
> around the 60 mark
> > > with
> > > no antenna plugged in at the back.
> >
> > It is possible -- even probable -- that the power supply=20
> filter caps,
> > and many other caps in the radio, are leaky and/or out of tolerance.
> > The filter caps can be re-formed: bring the rig up _slowly_ on a
> > Variac, starting off at something like 50VAC input.
>=20
> Great, thanks for the tip.
>=20
> > You know, I hope, that the chassis will be AC-hot (about=20
> 55VAC) if the
> > rig _isn't_ grounded, and that if it's pugged into a=20
> circuit protected
> > by a Ground Fault Interrupter, then the GFI will operate every time
> > you turn it on.
>=20
> I always use GFI's with my electronic equipment, it's become an almost
> anal obsession after grenading a KW1 I had when I was a kid. It didn't
> trip when I turned the rig on, and all of the tubes lit for a=20
> minute or two,
> but then some stayed bright and others were very dim, even though I
> turned the lights off in here, there was barely a glow.
>=20
> Before I turned it on, I took out al the modules and visually=20
> inspected
> them for signs of failed/failing components, and to my=20
> surprise, all of the
> resistors and capacitors appear to have been changed at some point,
> but unfortunately the disc capacitors weren't replaced with=20
> orangedrops,
> which is something I would certainly like to do. At the=20
> moment, however,
> I have very little testing equipment, so other than a visual=20
> inspection and
> electrical testing, I'm limited in what I can do.
>=20
> Thanks for your advice/help,
> Darryl
>=20
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>=20