With mine i used a 2n3055 for q4 driven by a bd139,this in turn drives 6x tip35 trannys,the transfo is one from a 30amp ham radio psu with 5 more turns on it,r18 is a selection of 3 different values selectable on a 3way rotary switch,the current sense resistor is 0.8ohm 25 watt wirewound,goes from 0-29v and 100ma to 20a ok,also quadrupled the size of the filter caps and used a 50a bridge rectifier,its working well,the heat sink is 8" square with a 12v quadbike radiator fan bolted to it runing from a thermo switch and relay,it has a cv led as well and a digital volt/amp meter with a 90a shunt.