Hi,
No Spice for me, just solder.

I hackt the schematic and below you can see the result for now.

Selecting and measuring the transitors with a cheap China meter, handy!.

Testing the current source and the zener with a variable power supply to see how mutch the zener voltage wil change.

I am now about half of building the circuit, the transistors 1 and 2 in the schematic are tight together for better thermal behavior.

I have adapted this version so that I can supply 22V and 2-Ampere.
If the circuit works, I will test the dynamic behaviour of this circuit.
The reason for using a modern power transistor is that it will then be easier to keep the circuit stable.
I have to confess that I have never built a Power Supply with a Darlington that has three transitors.
Probably there will be another HF stop resistor around this transitor.
Because I would like to have a reasonable noise / hum free design, the number of parts used is increasing rapidly.
And also three extra diodes for safety.
But be aware that with two opamps and a TL431 you can make a better power supply!

Why then all that effort to even build it, because I like to keep everything discreet and also just to play with it...
Depending on my work in the coming week, I will show the outcome of the above schematic.
Kind regards,
Bram