Darlington Pair Transistor Configuration

This a circuit of The Darlington Pair, on of popular transistor circuit configurations. Sometimes, this circuit is called the super alpha pair circuit. This circuit is used as power output stage. This circuit can give amplification of 10000 times. Here is the schematic diagram of the circuit:

The high amplification of this circuit due to the a change in base current of Tr1 and Tr2 that each of them cause a change in the emitter current 100 times larger. The base current of Tr2 is a emitter current of Tr1.