Abstract: Apparatus is provided for controlling the phase and speed of a motor for driving the rotary magnetic heads of a video tape recorder. An output of a signal generator, for example, a sawtooth wave, having a frequency corresponding to the rotational speed of the motor is compared with an external reference signal, for example, a 60 Hertz power line signal. A difference in frequency generates a varying error voltage whose polarity is indicative of the error direction. Relatively large or prolonged frequency errors result in an error voltage waveform having an abrupt and relatively large change. This error voltage is differentiated to create relatively large pulses of polarity depending on the direction of the error voltage. The relatively large pulses either charge or discharge a capacitor, the output of which changes the current to the motor so as to reduce the relatively large frequency error to a range suitable for handling by a conventional combined position and velocity servo system.

Abstract: A collector-loaded grounded-emitter transistor amplifier output stage employs a temperature-compensated bias network with an auxiliary transistor having its base electrode supplied quiescent current exclusively through a resistive element connecting the base and collector electrodes. A source of input signal is coupled to the base electrode of the auxiliary transistor by capacitative means and decoupled by resistive means from the collector electrode thereof. The temperature stabilizing auxiliary transistor accordingly provides a preliminary amplification of input signals for application to the base electrode of the output stage amplifier transistor, without use of additional active devices.