This very clever circuit will convert 1.5v to 9v to take the place of those expensive 9v batteries.
But the clever part is the voltage regulating section. It reduces the current to less than 10mA when no current is being drawn from the output. You can use two or three old cells for the supply and the circuit will totally use up all the energy from the cells. It's a great circuit for using up those old cells. With a 470R load, the output current is 20mA and the voltage drop is less than 10mV. It is best to use 3 old cells as this will deliver about 2.5v to 3v and the circuit will produce an efficiency of about 70%. Adjust the 15k resistor for 9v.
source : http://www.talkingelectronics.com.au/projects/200TrCcts/200TrCcts.html