Sound and light detector circuit to judge the quality of crystal oscillator

The circuit is as shown in the figure. It consists of a capacitive three-point oscillator, an emitter-follower isolation stage, a voltage doubler rectifier circuit, an audio sound generator, and a flash display circuit. It can detect the quality of the crystal oscillator. A good crystal oscillator will make a "beep beep..." sound, and LED1 and LED2 will flash and glow; a bad crystal will not emit any sound or light information.