[R-390] Autotuners

[Barry Hauser]

Drew wrote:

<snipped>
> Yes, the slip clutches were frozen with gummed-up lubricant and I did not
> force the movement.  Who knows what damage would have resulted had I
tested
> under motor power.  Disassembly, soaking in lacquer thinner, relubrication
> and reassembly corrected the problem.

Careful checking, soaking, re-lubing. is generally in order with these
things.  Also, Dave Medley advises to check the motor on the '391 -- 
brushes, commutator, etc.  I'm told there are motor repair shops that can
service these still.  May just require some cleanup around the commutator
and brushes and lubricating the bearings.
It would be good to know the correct lube to refresh those bearings - not
only for '391's but for a vintage power tool, etc.  Anybody know?  It has to
be something that soaks into the bronze without killing it.

> I don't think I used a synthetic lubricant; the process will therefore
have
> to be repeated in another 20 years or so.

The mechanical positioners, with sandwiches of rotating, rubbing pawls,
might benefit from silcone lube, but that doesn't seem to be as popular
these days.  The stuff I'm thinking of was very thin and its primary
attributes - super slipperyness AND does not tend to attract dust.  For
example, it was the lubricant of choice for those bars in line printers and
selectric typewriters that the print heads traversed on.  So it wasn't so
much the long-lasting, non-gumming properties as minimum friction where
large areas of metal were sliding and where dust could be a problem, as with
paper dust and fallout from printer ribbons.  The positioning units have
covers, but are not sealed in a '391.

The worm drive goes through several sintered bronze Oilite bearings.  These
are porous bronze bushings that were permanently lubricated.  But,
"permanent" generally assumes for the "life of the tool" or whatever, not
necessarily 50 years going on another 50.  Those bearings were pre-soaked in
a special lubricant -- but I don't know what.  I have one '391 where a
couple of bearings partially disintegrated ... with some bronze dust trails.
New bearings are still made -- but there are dozens of sizes.  The originals
are pressed into (maybe glued?) the cast aluminum frame.


> It would be a simple matter to lower voltage to the motor to reduce the
> torque for testing purposes (for the R-391, back on topic, whew!).

I doubt that it would work.  The '391 needs some minimum amount of torque to
actuate the contraptions or it will stall and malfunction..  However, you
gave me an idea.  Disconnect a motor lead.  Hook up a zero center meter or
DVM to the loose motor supply lead.  Power it up and change channels.  Use a
good Bristol wrench (like an Xcelite) to manually turn the worm drive shaft
in the correct direction according to the polarity of the meter reading.
(There is an access hole on the right side and a spline socket in the end of
the shaft for doing the synch procedure.  Make sure it's a snug fit as you
don't want to strip that socket.)

Offhand, I don't know which polarity corresponds to what direction, but that
could be figured out from the manual.  Part of the problem is that, under
power, the thing moves a bit too fast to figure out what may be wrong and
both KC and MC shafts may be turning at the same time.  By hand cranking it,
you can slow down to a crawl, look, listen and feel,  at what should be the
changeover or stopping points.  Since the motor is not running, you can use
a lower current supply -- anything strong enough to actuate the relay.  The
receiver itself can be turned off.

> I used an old Telco power supply salvaged from the junkheap for the
24VDC - no construction required there.

That' right -- improvise.  You can also rig a separate 24 volt supply line
and use it with a bench type P/S or temporarily borrow a supply from
something else of adequate current rating.  Chances are, even if the thing
works, you'll only use the autotune on special occasions, or periodically to
prevent "sticktion".

"Gentlemen ... Actuate your contraptions!"

Happy New Year to all
Barry