Single-tube LC self-excited oscillator circuit R1,R2,R3 constitutes the static operating point of BG1! L,C1 is a resonant loop! C2 is a positive feedback capacitor! C3 is the signal output. The instantaneous LC loop will produce a charge and discharge attenuation oscillating current signal! This signal is sent to the input end of BG1 through C2 to form a feedback on R2, and the signal is amplified and sent back to the LC loop to compensate for the attenuated signal, and this oscillation can be maintained. This is the principle of self-excited oscillation.