Crystal tester

  
Transistor Ql, a 2N3563, and its associated components form an oscillator circuit that will oscillate if, and only if, a good crystal is connected to the test clips. The output from the oscillator is then rectified by the two 1N4148 diodes and filtered by CI, a,01 µ capacitor. The positive voltage developed across the capacitor is applied to the base of Q2, another 2N3563, causing it to conduct. When that happens, current flows through LED1, causing it to glow. Since only a good crystal will oscillate, a glowing LED indicates that the crystal is indeed OK.
Crystal tester - schematic

The circuit is powered by a standard nine-volt transistorj*adio battery and the SPST pushbutton power-switch is included to prolong battery life.




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