Description:
A simple test circuit to fault find audio and radio equipment. Can be used to
inject a square wave signal, rich in harmonics, or used with headphones as an
audio tracer.
Notes:
A single pole double throw sitch is used to switch
between inject and trace modes. The diagram is drawn in trace mode, the
earpiece being connected to the collector of the last transistor. Both
transistors are wired as emitter followers, providing high gain. DC blocking is
provided by the 1n capacitor at the probe end, and the two stages are capacitively coupled.
when the switch is thrown the opposite way (to the
blue dot) both transistors are wired as an astable
square wave generator. This provides enough harmonics from audio up to several
hundred kilohertz and is useful for testing AM radio Receivers.
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