Magnet And Coil

In the ToneGenerator, magnetized rods, about 4 inches long and l/4 inch in diameter, are mounted near each ToneWheel. A small coil of wire is wound near one end of the magnet. The tip of the magnet at the coil end is ground to a sharp edge and mounted near the edge of the associated tonewheel. The rod can be adjusted closer or farther from the tonewheel to increase or decrease the amplitude of the output signal.

Each time a tooth of a tonewheel passes the rod, the magnetic circuit changes and a cycle of voltage is induced in the coil. The voltage is very small and the frequency is determined by the number of teeth and the speed of the rotating tonewheel. Larger coils are used with tone wheels of lower frequencies to provide good low frequency output, but smaller coils are used with tone wheels of higher frequency to prevent excessive losses. Copper rings are mounted on certain low frequency coils for the purpose of reducing harmonics. The eddy current loss in such a ring is small for the fundamental frequency of the coil, but is high for its harmonics. As a result, the relative intensities of any harmonics which may be produced by irregularities in the tone wheels are reduced. Most coils have an associated ToneGeneratorFilter.