Something that might be helpful to Bill Finch and Robbie:

Concerning pipe organ actions, tracker is the ideal for all historically
minded musicians, but little of this type of music is desirable for a
Band organ.  The beauty of the tone from the tracker system is the fact
that on the pipe side of the valve is a wind channel that goes up through
the chest past the stop boards, and then through the pipe toe 'til it gets
to the flue formed between the lower lip of the pipe mouth and the
languid or the floor of the pipe mouth.  (Notice how 'human' the pipe's
parts are named?)  The mechanism usually requires a 4"-10" channel from
valve to pipe toe.  This gives the pipe an air buffer that allows the
pipe to speak better.

In the direct electric action that channel is only as long as the
thickness of the pipe toe board as the valve is usually mounted directly
under the pipe.  The problems with voicing and pipe speech is caused by
the direct electric solenoid opening too fast and there being no Air
Buffer to cushion the pipe speech.  What happens instead is a blast of
air hits the flue and there is a big bubble of air that the pipe
overcomes before it can speak.

The electro-pneumatic system seems to work best or most pipe organ
systems today would not be still using it.  It is 100 year old
technology.  It's speed is controlled by the pressure of the wind to the
pipe which slows down the action enough for better pipe speech.  Now we
are talking about milliseconds, here so there is no reason to say that
this action is slow.  Only the pipe knows the difference.  Any of the
existing actions are lightning fast if they are in good shape.  The
complaints about slow pipe organ action is a myth.  Some of this is
because of the distance between the console and the pipe mouth.  (It may
sound a second late.)  My organ teacher, played Notre Dame before the
last rebuild, which is a tracker organ and she complained that she had to
play as if the organ was turned off.  (hearing it mentally)  It seems
that from where the organist sits, you must wait 6 or 8 second to hear
the note you just played.  IF the organ system is in "needs-a-rebuild"
condition the action works slowly.  I have proved this several times to
my satisfaction by rebuilding an antiquated system and it is like
lightning when you play it.

The Wurlitzer Theater organ action is probably the finest combination of
the tracker system and the electro-pneumatic systems.  It is far faster
acting than any other pipe organ action.  Even though it has lots of
relays to slow it down, the pipe response is one step faster than
lightning.  The valve is right under the pipe, but it is a pallet valve
just like in a tracker organ.  This is activated by a large pneumatic not
a pouch.  The pipe speech bubble is also taken care of because the toe
board of the chest is thick enough to incorporate an expansion chamber
between the pipe toe and the pallet valve.  This means instead of just
cutting a thick board and putting pipe toe holes in it, they built it up
with a thin board with an inch or two wide channel dividers .  The toe
board which is also thinner is glued to the top of all these little
channels and seals up a dead air space inside the toe board.  The
attached pneumatic action is so fast because the pressure used is far
higher than classical organs.  Most Wurlitzers play on 8" to 20".  The
larger organs playing into larger halls would be on the higher pressure.

I hope this helps.

D. L. Bullock   Piano World  (and Dallas Pipe Organ Service)   St. Louis