[R-390] 390() vs 390(A)

Tue Dec 28 21:30:05 EST 2004

All: I once had an ARC-38A and associated 180L-3 automatic tuner.  Autotune
mechanisms in both of those were typical Collins.  The most bizarre part of
the operation was the frequency control for the ARC-38A.  They used an
electromechanical phase-locked loop.  It was strange: the VFO frequency was
compared to a crystal-synthesized reference switched by the autotune
mechanism, and the VFO shaft was driven with a motor to match the reference.
The control loop was a proportional / integral loop!  Very strange...they
had crystals to synthesize the reference in 500 Hz steps...why not just use
that to control frequency???

Dave Maples

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of Michael Murphy
Sent: Sunday, December 26, 2004 10:51 PM
To: paul at pdq.com; Barry Hauser
Cc: r-390 at mailman.qth.net
Subject: Re: [R-390] 390() vs 390(A)

Before we leave autotunes: I have owned an ARR-15 /R-105 RX and an ARC-2
XCVR and they both had very nice (and similar) autotunes and tube lineups
for that matter. My guess is that they were sisters; contemporary mid 40's
designs. The late 1930's autotune in the ART-13 takes the cake though. When
I set that thing loose, it is a wonder to behold. I have a converted SCR-522
aircraft rig which had autotune, but I ripped it out in favor of local
controls. Anybody ever fired up one of those VHF autotunes with the 832's
and butterfly capacitors spinning up??

Mike Murphy WB2UID

----- Original Message -----
From: "Paul H. Anderson" <paul at pdq.com>
To: "Barry Hauser" <barry at hausernet.com>
Cc: <r-390 at mailman.qth.net>
Sent: Monday, December 27, 2004 9:40 PM
Subject: Re: [R-390] 390() vs 390(A)

> On Mon, 27 Dec 2004, Barry Hauser wrote:
>
> > Hi Roy & gang
> >
> > Well, if you get one, YMMV.  Odds are the autotune doesn't work -- and
it's
> > not a good idea to try it before overhauling the thing, no matter how
> > tempting.
>
> I agree!
>
> > the knobs down and rotate it.  However, it's not a complete simulation
as
> > the relay and control unit aren't doing their things. It's all
hard-wired
> > together -- including the relay -- no socket.
>
> Fortunately, the two mechanical tuning mechanisms and the control relay in
> the center are three independent units.  You can drop the front panel,
> remove the KC and MC mechanical tuning units and just work on the control
> relay alone until it and the motor appear to be working properly.
>
> The KC and MC units are nearly identical, but one is tapped for another
> screw, if I recall - I forget, but I think it is for the MC indent lever.
>
> > So, having one offers no assurance of comprehending how it's supposed to
> > work, let alone mastery.  You have to walk through the manual
explanation,
> > and that's lacking.  Actually, the equivalent manual section for the
R-105
> > (ARR-15?) does a better job.  The mechanisms are similar.
>
> It isn't too horribly bad, as long as you understand the failure modes
> (some of which you mention here).
>
> > The best procedure is to open up whatever you can, degrease, clean
contacts,
> > re-lube, see if things move, set the synch.  Then, make darn sure that
the
> > channel selector is set to the same number as shows in the window.
>
> Personally, I'd suggest starting with the motor and relay first.  You
> don't need to pull any wires.  Just drop the front panel, pull the two
> tuning units from the KC and MC side, then see if you can use the channel
> changing to do something (anything) reasonable with the motor, relay and
> channel indicator.
>
> Put the tuning mechanisms back in only after ensuring that the slip clutch
> in it is free.  From memory, I don't recall if you can do that easily.
> But making sure you've cleaned the whole mechanism of all crusty grease is
> a good step.  I soaked mine for a week each in kerosene.
>
> If the slip clutch does not slip, then you will discover a failure mode of
> the 391, which is that either the gear driving the long cross shaft will
> strip (if the oilite bearings are loose enough), or you will start
> breaking things in the RF deck or both.
>
> If the slip clutch does slip, then you're a whole sight safer, because the
> unit is designed to slip to a) prevent damage, and b) allow for the tuning
> to work (it tunes both KC and MC down to the low end 10 turn stop, and the
> slip clutch starts slipping in each tuner unit - that happens in
> association with the control relay to "reset" the tuning to a known spot -
> at the low end of the 10 turns).
>
> > new cordless phones.  Yup, it'll wreck yer deck -- if the vibration
doesn't
> > kill half your tubes.  (Make sure the filament in your ballast tube is
nice
> > and flexible before powering up.)
>
> I can't recall exactly which cam it is, but if the KC 10 turn stops aren't
> aligned, then the mechanical tuning can drive the cam to a point where the
> clamp may break.  I believe if the stops are correctly set for both the KC
> and MC mechanism, that there isn't anything the autotune can damage in the
> RF deck.
>
> > Poll -- how many of you guys have R-391's with working autotuners?  How
many
> > with non-working ones?  How many unknowns?  Actually, I think it was
Paul
> > who rebuilt his '391, right?
>
> Yup - got mine working - am working on another one.
>
> Basically, if your RF deck 10 turn stops are in alignment, and if the slip
> clutches are free, you can't easily damage your 391 autotune.  You'll know
> for sure if your slip clutches aren't free by the horrible gear grinding
> noise as the motor gear tries to strip the long shaft gear.
>
> Paul
>
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