When B is pressed in the given circuit, the capacitor (C) is charged. When we extract the butode, the current of electric charge accumulated on C passes through resistor R and triggers the transistor T1 and T2. Transmission switches on T2 transistor relay. After a while, the electric load on the capacitor plates will be cut off, the transistors will be cut off, the relay will return to its original position and the lamp will go out.
Since the resistance value of the transistor T1 connected to the base of the transistor is very large, the bellows draws a very small current. In this case, the capacitor discharges very long.