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MMD > Archives > April 2001 > 2001.04.22 > 03Prev  Next


Seek Replacement Small Variable Speed AC Motor
By Bob Pinsker

Dear people,  Thank you for the nice words in yesterday's Digest
about the research Mike Meddings and I are doing!  But today's plea
for advice and help has nothing whatever to do with Jelly Roll Morton
or J. Lawrence Cook.

In the 2001.03.20 MMD, there was a description by Tom Lear of the
simple speed control circuit and induction motor used in the Dynavoice,
and an answer from our Learned Editor about how it worked.  It so
happens that very late last night I blew up a motor very much like
that, this in the spool box from a 1950's or 60's player piano.
I don't know any more than that about what it came from, other than it
was evidently a solenoid player, as I have a photocopy of the schematic
(it says "?203 Player Piano Schematic", where the "?" is blurred; it
could be a "1").

Anyway, I have increased the resistance across the diode, just as Tom
Lear reported, to slow down the motor, but evidently the torque that
it can supply decreases substantially at way below synchronous speed,
I guess, because the roll got stuck, the motor started to smoke, and
before I could shut it off (and before the circuit breaker opened) the
motor blew up!

I took it apart this afternoon, and found that one of the connections
to the coil is just plain gone -- the coil reads an open circuit --
and when I unwrapped the tape, which was all burned and smelly, one of
the two connections between the leads and the coil has disappeared.

So I guess I have to replace the motor, or at least the coil.  Several
questions arise:

1.  Is there any hope of finding an exact replacement?  Yes, of course
the thing is probably 40 or more years old, but I guess there's a huge
amount of experience in this gang on fixing things that are a heckuva
lot older than this!  The motor says the following on the label on the
coil:

  GI 51335-30
  115 V - 60 Hz
  660273-01
  190-7440

2.  If this is impossible to replace one-for-one, can one replace the
coil somehow?  The plastic at one end of the coil has embossed on it:

  29809 - 03

The problem with this, other than finding the coil someplace, is that
the laminations are riveted together, and I guess I'd have to drill out
those two rivets to get the coil that is linked to the laminations off
and the replacement in, and I suppose I'd have to somehow replace those
rivets.

If I can do neither of the above, then I'll have a bit of a problem
trying to get this thing working with a more modern motor, as there's
a gear box and everything.  I guess one of the advantages of this type
of motor is that when the coil is not powered, a spring pushes the rotor
out of the laminations, thus neatly disconnecting the rotor from the
gear train and freeing the roll take up from the motor for rewinding.

Any advice would be appreciated!  Thanks!

Best regards,
Bob Pinsker
San Diego, CA


(Message sent Sun 22 Apr 2001, 21:49:17 GMT, from time zone GMT-0400.)

Key Words in Subject:  AC, Motor, Replacement, Seek, Small, Speed, Variable

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