Quartz crystal selection circuit

As shown in the figure, BX is the quartz crystal to be tested (also known as crystal oscillator). Plug it into the sockets X1 and The oscillation signal is output from the VT1 emitter, coupled to VD2 via C3 for detection, C4 filtering, and becomes a DC signal voltage, which is sent to the VT2 base, causing VT2 to conduct, and the light-emitting diode H to emit light, indicating that the quartz crystal under test is good. If H does not light up, it means the quartz crystal is bad. By appropriately changing the capacitance values ​​of C1 and C2, it can be used to test quartz crystals of different frequencies.