Above diagram is the scheme of variable DC power supply with output range of 1V to 17V. This power supply is used very few components, the power supply will be so easy to build. Serial power transistor which will be known and popular 2N3055, power supply has a voltage control and current. The source of alternating voltage is 24V transformer.
This circuit used Integrated Circuit / IC LM723, also known as UA723 which is a dedicated integrated circuit design and manufacture a wide range of stabilized power supplies. If you have little hold on the label of the integrated circuit 723, then you would find between different manufacturers may find some other designation, all of the total number of 723 in the middle of the whole label.