This circuit is an astable multivibrator, or oscillator. The two transistors are cross-coupled in such a way that the circuit switches between two states. In one state, the base of Q1 is about one diode drop above ground, allowing base current to flow. This keeps Q1 on in saturation, allowing current to flow through the collector, keeping Q1's collector voltage low and discharging C1. Q2 is off because its base voltage is not high enough to turn it on. As collector current in Q1 flows through C1, the base voltage for Q2 rises until it is high enough to turn Q2 on, causing current to flow through its collector, which lowers the collector voltage (the current causes a voltage drop across the resistor above it). The right side of C2 dropped, but the voltage across it did not change, so the base voltage of Q1 drops below ground level, turning it off. Then we get the other half of the cycle, with current flowing through Q2. This continues until Q1 turns on, and then the cycle repeats.
This page is a utility for simulating астабильный мультивибратор (генератор) online with specified initial values.
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