Anatomy of a WurliTzer Theatre Pipe Organ
The relay operates by causing the chopper bar, attached to the
pneumatic, to come down across each of the wires on the contact
blocks, creating a short between all the contacts. The pneumatic
is forced closed by the air pressure in the chest when the valves
operate to open the channel from the pneumatics to the outside air.
On each contact block one contact is wired to the common power
supply that runs behind the contact blocks on top of the
wiring spreader strip. When the relay is activated power goes
through these contacts to the shorting bar and over to each of
the other contacts.
The other contacts on the blocks are wired to the stop tab rocker
switches on the switch stack. There is one wire from each note
relay going to each stop switch. There are enough contacts on
each note relay for the number of stop tabs on the console for
the relevant keyboard.
The large screws in the top of each pneumatic are to adjust the
limit of the downward movement of the pneumatic and the chopper bar.
It needs to be set to ensure that there is enough movement so that
all contacts are touched by the bar, plus a little more to provide
a wipeing action on the contacts to keep them clean each time they
operate. Too much movement and there will be extra wear on the
contacts, the wires will be flexing excessively causing fatigue and
breaking, and it will ake longer for the contacts to open when the
note is released making things slow.
The buffer pads above the pneumatics are attached to the threaded rod
through the rail above. These set the limit of the upward movement
of the pneumatics. They need to allow the pneumatic to open enough
to lift the chopper bar clear of the contacts. Too much movement
increases the time between when the note is played and when the
chopper bar touches the contacts which also makes things slow.
Properly adjusted there should be as small amount of movement as possible
so that the speed of the relay is at its maximum. The maximum speed
is remarkably fast.