One big mess of resistors, transistors, and a few capacitors. The 100uF capacitor could be a bit bigger to better stabilize the constant current source, but as long as it works it should be fine. It constantly consumes an average if 97W. Since it outputs up to 20W, it has an approximate efficiency of 20%. This is at least reasonable if not good for this style of class-A since the maximum theoretical efficiency of this style of class-A is 25%.
