Here is a simple and economical 10A variable power supply with 1.2-30V. LM317 have been used to drive 3 NPN TIP41C transistors (or three 2N3055). Nothing to say about the project, it is really simple. The main supply must be connected to a rectified source (transformer + 20-30A bridge rectifier). For Q1,2 and 3 can be used any power TO220 transistor (TIP132C,TIP41C etc) or three external 2N3055 transistors. The three 0.1ohm resistors are 5W resistors. The Tip41C supports upto 6A with a collector dissipation of 65W max; a cooler is a must. If an higher power is needed they can be replaced by three external 2N3055 (115W). Pad1 and Pad, if an amperometer is not used, must be short-circuited.