While browsing the lab power supplies market and watching the price ranges, I've decided that I'd be better off with building my own, since I've got most of the needed parts anyways.
I've searched for schematics and stumbled across the one included below. It is self-explanatory in many ways, but there are two questions that keep bothering me.
The lower part of the schematic with the LM377L regulator handles the negative power rail for the TL082. I completely understand why is it needed when using the TL082 opamp, as it is not a rail-to-rail opamp.
The first question is: Why not just use a LM324 rail-to-rail opamp, for example? Will there be any drawbacks?
The second question is: Why is the BD139 transistor on the right part of the schematic needed at all? If it is there to increase the current gain - aren't there any high-power transistors with higher hFE that could be used instead of suggested 2N3055?