The long wooden boxes on which the pipes sit, and which contain an array of valve mechanisms (the 'action') for admitting air to each pipe.
The action and its connection to the console may be purely mechanical ('tracker'), or assisted by pneumatic and/or electrical means. Almost invariably, theatre organs use electrical means to transmit the signal from the console via the relay, and pneumatics to amplify the signal to open the valve ('pallet') that admits air from the windchest into the pipe.
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