I am restoring a Pratt-Read player mechanism, with an unusual device
under the spoolbox that I am guessing is some type of pneumatic
tracker, but for the life of me I can't figure it out.

Directly underneath the spoolbox shelf is a long horizontal pneumatic
connected directly to the stack vacuum. When the upper moveable leaf
closes down, linkages connected to this leaf slowly pull the left and
right take up spool flanges (which are floating and free on the take-up
spool axis) in toward the roll edges on either side of the take-up
spool.

What I don't get is that the take-up spool, tracker bar, and top roll
chuck are all fixed and cannot move left or right to adjust tracking.
If this is a tracking pneumatic, I can't imagine how it could do
anything at all as far as adjusting the roll alignment.

Can anyone shed some light on this for me?

John D. Rutoskey