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21 Note Trueman Street Organ

The organ is powered by a hand operated crank handle. This works the bellows to pump air into the wind-chest and also feeds the perforated card book through the sensor mechanism. The cards have 21 lines of holes, one for each organ pipe.

Mounted on the wind-chest are 21 air-valves, normally held in a closed position by air pressure, with each valve linked to the sensor mechanism by plastic tubing. When a hole in the card passes through the sensor, the air pressure at the air-valve drops and opens the valve to allow air from the wind-chest into the organ pipe to produce the musical note.

An example of the perforated card that controls which pipes are playing is shown below. Each fold or page is 6.5" x 3.25".