Elenco 130-in-1 Electronics Playground - Manual (Page 139)

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This experiment is a simple transistor audio amplifier
used as an audio signal tracer. You can use this
amplifier to troubleshoot transistor audio equipment.
You can connect the wires to different terminals in the
circuit until you find the stage or component that does
not pass the signal along when a circuit is not working
correctly.
The 0.1
μF input capacitor blocks DC so you can
probe around circuits without worrying about
damaging the circuit.
The amplifier circuit is a common-emitter type. The
transistor’s emitter is connected directly to the input
and the output of the earphone. Its base current is the
self-current type. The current from the transistor
collector provides current to the base (through the
470k
Ω resistor). This provides some stabilizing
negative DC feedback.
You can use this amplifier to check any transistor
radio or amplifier you have that needs fixing.
Notes:
EXPERIMENT #117: AUDIO SIGNAL HUNTER
Schematic
Wiring Sequence:
46-110-94
47-79-93-EARPHONE
124-48-PROBES
119-80-EARPHONE
109-PROBES
121-122