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 switch 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
capacitive 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.
