The purpose of this is to compare and learn different circuit topologies, not use of the shelf solutions which obviously provide cheaper, simpler and better results. Considering this requirement (no use of ICs, not even a matched pair), the parameter ranges given below and that the load should be connected to the voltage source:
Can we get better temperature stability and input voltage regulation by an order of magnitude (e.g. < 100uA)? To focus on the main goal, let's disregard the temperature coefficient of the metal film resistors.
The load regulation of the circuit on the left is already good enough. I've used different BJTs on the right do avoid depending on any form of matching between the discrete components.
The parameters are: 10 <= Vin <= 30, 0 <= Temp. (C) <= 50, 0 <= RL <= 1200, Isource ~ 5mA
Manually adjusting the central value with a trimpot is fine, let's not add this concern either.
Note: the ranges below are simulated by fixing all but one parameter.