I encountered this unusual tracking mechanism for the first time in
a Pratt-Read I completed last summer.

This type of tracker consists of a regular, large horizontal pneumatic
mounted directly under the spoolbox.  The pneumatic is connected from
the center of its moveable top board by a leaf spring fixed with a
cotter pin jointly to a pair of levers, which are then directly
connected to a pair of moving forks which ride against the metal
take-up spool flanges.

The flanges are able to move freely on their own on the take-up spool
axle, and with the player at rest, they are held approximately 1/4 inch
away from the edges of the take-up spool core by light coil springs
between them and the take-up spool core.  The control of the flanges by
these forks is mostly hidden by wood covers inside the right and left
spool box walls.

The pneumatic centers the roll by slowly and gently closing the take-up
spool flanges simultaneously toward both edges of the roll as soon as
suction is supplied.  It is very simple in operation, and actually
works very well if the edges of the paper are in good shape and the
holes are correctly aligned in the roll.  I was rather impressed.  The
tracker operates during play mode of the piano only.

The pneumatic needs to be removed from the mechanism by removing the
leather nut connecting the linkages to it, then removing the one screw
on the right-hand side mounting bracket.  The left side of the pneumatic
has a pair of pins only, so it slides right out after disconnecting the
suction 5/32" line.

The pneumatic has to be recovered, and it _must_ be airtight.  There is
no room for error with this -- if it leaks it will not have the power
to do the job.  It has a 5/32" suction supply, and if it leaks at all,
it will not be able to overcome the spring which holds it open, and it
will not have enough power to move the flanges.  _Don't_ bend the leaf
spring connected to the linkages.  It will break in an instant -- don't
bend it at all.

The take-up spool must be removed from the spoolbox, and the axis
cleaned and polished.  The bores in the take-up spool flanges have to
be completely clean and gunk-free also.  Just put a drop of light oil
in the bore of each one during reassembly, and use a little Lubriplate
on the forks.

There is a junction block directly to the left of the pneumatic where
the supply tubing changes from 3/16" to 5/32" that contains a screen
and a gasket.  Replace the gasket, and make sure the screen is clean,
and that the screws on the cover are tight.  Reseal the nipples on the
connection block as well as the nipple on the pneumatic with burnt
shellac.

If everything is reassembled and moves freely, but the pneumatic still
doesn't bring the flanges in contact with the roll edge on quiet
playing levels, then something is leaky.  I cannot stress enough how
important it is in this unit that everything is airtight for it to
work.

I hope this information helps.

John D. Rutoskey