"When developing the PRO-3, John Fisher measured his 147. He found that the top rotor had a rotation speed of 400 RPM on Tremolo and 48 RPM on Chorale. This was with the belt in the middle pulley position and with a normal belt tension. The lower drum rotated at about 342 RPM on Tremolo and 40 RPM on Chorale."

(http://www.theatreorgans.com/hammond/faq/hammond-faq.html)

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