Two Simple Crystal Test Circuits

Posted on Feb 5, 2014

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

Two Simple Crystal Test Circuits
Click here to download the full size of the above Circuit.

which may be adjusted with the preset. 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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