[R-390] Autotuners

[Drew Papanek]

Hello,

Sandy Geiger expressed misgivings about firing up the autotune on his 
Mish-restored R-391:

>Guys-  I  have  an  R-391,  s/n  282,  that  I  got  from  Rick  Mish.
>Electronically,  it is tweaked to the nines,as all Rick's restorations
>are,  but  I've  never  been  brave-or  foolish-enuff  to  fire up the
>Autotune.  Rick  kinda suggested it would be in my-& the radio's- best
>interests  if  I  left  it  alone.  Too  many  tales  of R-391s eating
>themselves have convinced me this is the right thing to do.-Sandy G.

He cited Barry's observations:

>It is impossible to walk this gizmo through manually in  steps, though you 
>can put a bristol wrench in the synch >adjuster,  lock 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.

I was able to manually operate the autotune and exercise the electrical 
portion of an ART-13 by mechanically disconnecting the motor from the rest 
of the autotune.  With power applied and channel selected, the motor would 
run until I had turned the shaft (many turns!) to operate the limit sensing 
switch, whereupon the relay would pull in and the motor would reverse; 
running until I had turned the shaft enough(the other direction) to operate 
the channel position sensing switch (too lazy to go get the manual and see 
what they call those switches).

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.

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

There is a special tool for turning the ART-13 autotune line shaft; I did 
not have the tool but it was a simple matter to make one up.

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

Drew