HAMMOND TONE-WHEELE&MP 88.014 Music Recording - Electronic June 1937 Close-up showing a Hammond tone-wheel. The wheel has convolutions on the rim and in operation it revolves close to the magnet such as shown in the photo. In the coil of the magnet is set up a tiny alternating current corresponding to the number of convolutions that pass through the magnetic field in a second. Thus 440 vibrations would give A on the international music scale.
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