What transformer to buy?

Choose a better pass transistor! 2N3055 has so little gain at high current. NJW3281 will hold its gain up to 7A for instance, the 2N3055 gain starts falling rapidly above 1A.


At 5A output the 2N3055 will need about 150mA base current, something like the NJW3281 only 50mA - which would allow the LM317 to go without a heatsink.