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Two Crystal Test Circuits

Circuit: Andy Collinson

Description:
Two simple test circuits to check operation of quartz crystals.

Test Circuit Diagram 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. The more active the crystal, the higher the output deflection which may be adjusted with the preset.

Test Circuit Diagram to Check Operation of Quartz Crystals 2

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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