With the original design, using a lower voltage transformer (i will not obtain 30V but who cares!!!), i want to pus BD139, what modifications i need to do? What is the scope of Q1 in the original schematic? If i put BD139 and keep TL081, did i need to do modifications? What are those? The recomanded opamps in the newer version is expensive in comparasion with TL081! If i understand well, for 5A, i need 4 output transistors to keep up with the current, and a better rectfier!