This circuit from the 70s, was found in a publication from the 70s, we kept the original text. Operational amplifiers often require power that has a central negative voltage and identical powers, but of opposite polarity. This is exactly what the current source of 15-0-15 volts does. If we take the positive 15 volts to the center (earth) we will have 15 positive volts in relation to the earth. At the other extreme, we will have 15 negative volts in relation to the earth. From end to end we will have 30 volts. The current that this circuit can deliver is' 30 mA.
LIST OF MATERIALS
C1 - 1,000 uF x 50 V. Electrolytic
R1 = 10 ohms, 1/2 w.
R2 - 470 ohms 5 w.
D1 to D4 = BY 126
D5 and D6: Zener diodes for the desired voltage
T1 = transformer 30 volts x 50 mA
S1- SPST Switch
