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 tonewheels of lower frequencies to provide good low frequency output. Smaller coils are used with tone wheels of higher frequency to prevent excessive losses. Copper rings are mounted on some low frequency coils for the purpose of reducing harmonics. This reduces the eddy current loss at the fundamental frequency of the coil. As a result, harmonics that may be produced by irregularities in these tonewheels are reduced. All coils also have an associated ToneGeneratorFilter.