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The paper describes an experimental ac motor alternator assembly which produces an output frequency exactly equal to a low-power secondary standard frequency signal source, such as a tuning fork or crystal oscillator. The frequency-controlled system employs a synchronizing type of control in contrast to the more generally employed error-detecting systems. As a result, no error exists between the output frequency and the secondary standard. The control system requires only low-level signal power from the secondary standard reference. The main synchronizing power is drawn from the unregulated feeder line. No mechanical devices are needed for frequency correction or synchronization. The synchronizing system is completely electrical, requiring no mechanical or hydraulic compensating devices. The mechanical components employ only a single moving party composed of rotor shaft and two bearings. The electrical energy supplied to the rotor is magnetically induced across air gaps so that no sliding contacts or brushes are used. Transient loads applied to the system do not produce any frequency transients; in other words, transient and steady-state frequencies are identical. Characteristics of a 500-va experimental unit are presented.