Description:
Two simple test circuits to check operation of quartz crystals.
Notes:
In the first circuit, above the BC548 is wired as a colpitts
oscillator, the frequency tuned by insertion of a crystal. A good crystal will
create high frequency oscillations, the output at the collector is rectified by
the germanium OA91 diode and a deflection will appear on the meter. Thw more active
the crystal, the higher the output deflection which may be adjusted with the
preset.
Notes:
The next circuit uses a working crystal again used to control the frequency of
a colpitts oscillator. This time the output from the
oscillator is taken from the emitter and is full wave rectified, the small dc
bias will then directly cause the second BC548 to light the LED.
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