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Why do you want a third transistor?
I use LTSpice. Its primarily a simulator but I find the schematic editor pretty useful. Best of all, its a FREE download from Linear Technology. Recommended.What software do you use? To draw a schematic
I didn't find LED in OrCAD Capture
The problem is this: The circuit above does not work. It freezes.The 2-transistor astable circuit can be extended simply to use any even number of transistors. Attached is a 4-transistor astable. The 'on' time of each LED is about 0.6*C*R where, for each stage, C is the capacitor value and R is the value of the resistor connected between +V and the transistor base, i.e. about 0.5 sec for the values shown.
The problem is this: The circuit above does not work. It freezes.
You need an odd number of transistors to create the "run" effect: