How multi-resonators workb

Figure (a) shows the situation when switch sl is turned off. Positive voltage is added to the base of VT2 from the power supply through R2 , causing V-12 to conduct. At this time,
the dotted line in the circuit is the current charging capacitor C2.
    Then make the switch sl close t as shown in figure (b). Since the capacitor C2 has been charged at this time, the voltage is reduced to o. Therefore, at the moment when the switch is closed,
it is equivalent to adding negative voltage to the base of VT2, causing VT2 to cut off. The direction of the dotted line in Figure (b) is the direction in which the charge of capacitor c7 is discharged.
Then the base voltage of VT2 changes from negative to positive, and then VT2 is turned on again.