I know that many of you have the book, The Art of Electronics,
this question deals with the circuit from fig 2.75 on page 105.

a zener diode and two transistors, along with 3 1K resistors.

I thought I would try to make this circuit, but I couldn't get the
exact components, and I thought great, this will be a learning
experience, LOL

this is pretty stupid, but maybe some of you will help out

Q1 - 2N3055
Q2 - 2N3904
D1 - 1N4731 4.3V
R1,2,3   1K


I substituted a TIP3055 for the Q1 2N3055
are these even close?

a MPS3904 for the Q2 2N3904
??

and a 1N4733 5.1V  for the 1N4731 4.3V

my input voltage is 15vdc and I get 5.5vdc output

what I'm really wanting to know is, what is the most important
component for determining the output? is it the diode? if so, why?

I rekon if these transistors are just variations of the ones called for
in this circuit, then the resistors are the same, the diode must be
the deciding factor?  but the circuit claims to regulate 12 to 25 v input
to 10 v output, so my 5.5v out is way off from this, so does a difference
of a 5.1V zener versus a 4.3V zener make this much of a difference?

thanks

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