Shared Dual Variable Power Supply
Most of the times a Dual Variable Power Supply is highly needed for electronics hobbyist at minimum expenditure. The circuit used here uses two numbers of LM338 in parallel, as Positive Voltage regulator and two numbers of LM337 in parallel, as Negative Voltage regulator.
Single Variable Resistance (5K Volume Control ) is used to control Positive voltage, which controls the output of both the LM338 in parallel. Similarly another single Variable Resistance (5K Volume Control ) is used to control Negative voltage, which controls the output of both the LM337 in parallel. Having parallel voltage regulators shares the load current and less heat is generated at higher currents. Heat sinks are mandatory and insulation should be used for all the four ICs.
Refer full circuit diagram: (TP1 to TP8 are Test Points to check the input and output voltages)
Once the components are soldered as per the circuit diagram, then connect +35V, GROUND & -35V Power supply to the board and confirm that the power LEDs are glowing.
Connect common terminal (black) of multimeter to ground of the circuit. Now, check the varying output voltage at TP4 and TP8, by changing the resistance of VR1 and VR2 respectively.
Similarly, observe equal voltage change at TP2 & TP3, while varying the resistance of VR1. Again, observe equal voltage change at TP6 & TP7, while varying the resistance of VR2.
GOOD LUCK. ENJOY.