power supply regulator mini 9V 0.75A by Transistor BD242 and BC549C.
VR1-1K control Volt output.VR2-1K control current output.
If you have old equipment from tape radio will to do good.
I advises that try bring build , mini power supply 9Volt all right.
By I uses the transistor number BD242 , the diode the ordinary and
part the other a little again. It can help modify voltage 12VDC from be 9VDC 0.75A .
For VR1 and VR2 use for fine decorate voltage and current can follow want.
You can see the detail can add in the circuit.