Could somebody please copy this pastel schematic and increase the contrast so it can easily be seen?
It appears to have no error correction amplifier with negative feedback so its voltage regulation is horrible.
Its transformer is 18V x 3A= 54VA. The 18V transformer has a peak voltage of 25.5V. The load on the transformer is 25.5V x 3A= 76.5VA so the transformer will be overloaded.
The 25.5V peak voltage is reduced to about 23.5V by the bridge rectifier and the small value of the filter capacitor reduces it more. The maximum base-emitter voltage of the TIP31 transistor at 3A is 1.8V so the maximum output voltage at 3A is less than 20V.
The 27V zener diodes will do nothing.
The maximum base current of the TIP31 transistor at 3A is 300mA which will burn up the pot R10. The TIP31 will burn up if the circuit works and the output was 0V at 3A because then the transistor must dissipate 84W or more.
The five 1 ohm resistors in series with the output and the two diodes will cut the output voltage and current.