Dear Joe, Greetings from The Bronx.  The Orchestrelle Company was
the European counterpart of the Aeolian Company of the U.S.A.  The
Themodist system was the forerunner of the Duo-Art system.  The former
system only accented the theme through the "snake-bites" at the edges
of the playing notes, whereas the latter system not only controlled
these but also controlled and varied the vacuum pressure automatically
from additional ports above the first 4 notes in the Bass section and
the last 4 notes in the Treble section (tracker bar would have a full
complement of 88-note ports).

In the former system the pianolist would have to follow a Theme line
and accenting instructions printed on the roll to best recreate a live
performance.  The latter system was available in what is referred to
as a Half-Duo-Art, or a Full Duo-Art.  In the Half-Duo-Art, the system
required the assistance of a pianolist to pump the treadles to create
vacuum to power the system and to also follow a printed Theme line on
the roll.

The Full Duo-Art, or Electric Duo-Art, on the other hand has either a
rotary pump, as in later instruments, or what is known as a "Steamboat"
pump (an elaborate and complex vacuum pump much prized by collectors
today) (Both are powered by an electric motor).  The only requirement
for the pianolist was to load the roll, set the tempo, place the roll
transmission into play, and switch on the power.

Both the Themodist and Duo-Art player actions have was is called a
'split-stack', whereas it was divided into Bass and Treble sections.
The "snake-bites" on the Bass end of the trackerbar caused the Bass
side of the player action to be accented, while the "snake-bites" on
the Treble side caused the Treble to be accented.

The possible reasoning why three notes on the 85-note trackerbar were
plugged, was perhaps the former owner was playing Duo-Art rolls instead
of Themodist rolls.  The control perforations were causing errant notes
to play, so the easiest fix would be to plug the offending trackerbar
holes.

The Duo-Art system has a cut-out switch in the spoolbox: Duo-Art On,
Duo-Art Off, and in between is an Arrow (this has been concluded to
cause the Theme ports to be activated without activating the Duo-Art
expression ports).  In the earlier full 88-note Duo-Arts, when the
switch is set to Duo-Art On, there is a 4-note cut-out pouch unit on
either side of the spoolbox.  These turned off the first four and the
last four playing notes on the trackerbar (the Duo-Art system was
limited to only 80 playing notes).  With the switch set to Duo-Art Off,
a pre-determined playing level was activated to play standard 88-note
rolls.  Later Duo-Art pianos did away with the cut-out pouches by making
the player stacks with only 80 valves and pneumatics.

Hope this helps,
Sincerely,

Dale F. Rowe
Bronx, New York, USA