As many are probably aware,  one of the more common Duo-Art tracking
devices contains the familiar double pneumatic which has a supply
nipple, along with two nipples which hook up to a cut-out pouch block
on top of the theme box, and which then are routed, through tubing,
to the treble and bass tracker triggers mounted in front of the
tracker bar.

Recently however, I have come across two earlier spool box assemblies
(both manufactured before 1920), in which the theme box is somewhat
longer than the more conventional one.  In one of them, the theme box
contains two additional outside valve assemblies which appear to have
connected to the tracker pneumatic without the benefit of the cut-out
pouch block.

In the other spool box assembly, the theme box is also elongated and
contains the additional two outside valves; however, the tracker and
supply holes were covered over with what looks like factory cloth,
rendering these valves inoperative.  However, mounted on the top of
this elongated theme box is the more conventional tracker cut-out pouch
block to which the tracker was connected.

I was wondering if anybody knows the background of the apparent
change in the theme box configuration and/or has any other information
concerning how the earlier double valve tracking device worked, as
opposed to the configuration of the tracker with the cut out pouch
block.

Please forgive me if this has been discussed before, but I just
recently came across these earlier theme boxes.

Barry Dennis