Better version: http://everycircuit.com/circuit/6558614509322240
Adjust the potentiometer to get an output voltage between 1.27 and 12.6 volts.
I haven't tried it on the breadboard yet so I don't know if it works properly, but it seems fine here with ideal components.
The circuit works with a BJT as the pass transistor as well. A base resistor would not be required since the op amp would take care of supplying the right amount of base current.
