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

[Paul H. Anderson]

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