There are two variants of the pedal-only ("half") Duo-Art of UK
manufacture. The simplest have two theme secondary valves and need the
Themodist sliders to be held fully over for playing Duo-Art rolls. These
instruments are pretty well identical to normal Themodist Pianolas with
one simple addition, namely setting of the Accompaniment level from the
roll. Many of these instruments use 80-note stacks so the only thing
needed for 'Pianola' mode is to block the accompaniment coding.
There is a more complex version of this instrument that doesn't require
the Themodist sliders to be held across, but contains an extra pair of
valves in the expression box to automatically block the direct air path
when in Duo-Art mode. There is a bit more complexity in the logic
switch in the spoolbox to operate these extra valves.
If either of these comes with an 88-note stack, there will be slightly
more complex cutout blocks to connect the top and bottom four tracks
between playing notes or operating the accompaniment level.
The Pedal-Electric Duo-Art [PEDA], on the other hand, is a full Duo-Art
installation with extra valves to allow the theme-accenting to operate
either from the Theme regulator (for Duo-Art playing) or directly from
the suction supply (for Themodist operation) -- a far more complicated
thing all together. I wrote an article about it some years ago for the
Player Piano Group Bulletin, which I've just put onto my web site,
www.pianorolls.co.uk, for anybody who might be interested.