Opening SA, changes the indicator lamp from flashing to steady-lit condition. The 6-V incandescent lamp on the collector of Q2 requires about 0.3 A. A 1-KO load resistor limits Ql`s collector current to about 6 mA.

The circuit is, therefore, asymmetrical with respect to the on currents of the transistors, allowing use of a much smaller transistor for Ql than for Q2.

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