A very simple variable
power supply circuit can be made using this electronic circuit diagram
.This variable regulator circuit will provide an variable regulated
output voltage , between 0 and 50 volts . The CA3140 operational
amplifier compares the regulator output to a reference voltage , that
depends on the R9 value.
The output voltage will be nominally twice the voltage between the
positive input ( noninverting ) of the CA3140 and ground . The
unregulated input voltage must be around 60 volts The output voltage can
be set between 0 an 50 volts using R9 potentiometer .The 2N3055
transistors must be mounted on a heatsink , to prevent the overheating
of transistors .