can you be more specific like input range voltage and current and similarly you output requirements
Its a somewhat complex schematic!
must work friend show me your circuit that didn't work may be we can help you .
Check out LM338.
Not going to get much simpler than that.
You will have to add more external stuff if you want to be able to set a current limit
below 5A , but that can come later.
Sorry , didn't see the 50V rating.
Try a lm317HV with external pass transistor. Still pretty simple!!
i've made 30v power supply few years back i'll give you diagram you have to wait may be tomorrow i am outside my work station ok