I'm having trouble with this same unit. Can anyone tell me how to increase the current output? One channel outputs 5.7A, but the other only outputs 4.6A. Probing around, the "bad side" has a higher Vce on all the 2N3055 pass transistors, so I'm assuming I need to increase the base current somehow. The zener V11 also has a higher voltage drop on the bad side. I tried reducing R4 but that did nothing. Would a lower voltage zener help? I guess I can't really follow the circuit well enough to figure out what's happening. Maybe if the op-amp output a higher voltage, it would allow more into the base of the 2N3055's?
Anyway, as advanced payment, I'm going to teach the forum how to add fine adjustment control to this style of power supply. Simply remove the board-mounted trimpots and replace them with panel-mounted trimpots. I'm using a 10k pot for the voltage (which makes the main voltage knob go from zero to 5v, instead of zero to 30v), and a 500k pot for the current (which makes the main current knob go from zero to 100mA, instead of zero to 5A). With this simple modification, you can easily adjust the current to a tenth of an mA, which is essential for doing LED testing where you want to set it to exactly 3.1mA, or 8.7mA.