This should come under the heading, "If you haven't run across one yet,
you're gonna".

The Wurlitzer company "manufactured" a player piano in the sixties and
seventies, and maybe into the eighties, I am not sure.  I put the
manufactured in quotes because they built the pianos, and someone else
made the player mechanisms.  They were and still are, when you find them,
a hairy piece of machinery.  Wurlitzer's players had to play the regular
88 note rolls, but they did not want to build, or have built, a pneumatic
action...  well not TOTALLY pneumatic.

The rolls were read by vacuum and the keys were played with solenoids.  How
it was done is a repairman's nightmare.  The tracker bar was very wide, top
to bottom, and well it should be.  Behind the holes in the bar, is an air
tight chamber containing small...really small switches.  This chamber is
under vacuum, and when atmosphere is admitted, the diaphragm under each
switch inflates closing the contact and sending the electricity to
solenoids under the keybed.  I have an original factory service manual for
them.  Fortunately, I have only run across two of them in all these years.
I was called to repair one a few weeks ago, in a piano store.  When you
turned the thing on, there was a high pitched scream eminating from the
vicinity of the tracker bar.  A tiny leak had developed in the cover of the
bar and that is what was making the noise.  Factory says... fill with
silicone.  I did... noise stopped.

The player units were made by a company called:

        Dale Electronics
        Yankton, South Dakota

These units were their model E-5.  Guess 1-4 were the prototypes.

Ed