Variable DC Power Supply

This power supply is based on the LM317 Variable Regulator. The input of the regulator needs to be around 28 Volts DC and it will output a DC voltage from 1.25vdc to 25 vdc. To adjust the output voltage simply turn the 5k ohm pot. The regulator will supply 1.5 amps of current.

From : http://home.maine.rr.com/randylinscott/apr20.htm