lu6etj wrote in
:

....
I should tell owen he was inadvertently moving towards a logical
bifurcation's fallacy because is not absolutely true that Thevenin
theorem can not be used to calculate -for example- circuit efficience.
There are an exception to this limitation = It can be used to
efficience calculations when disconnecting the load in the original
circuit the dissipated power is null.

Miguel, when I said "cannot" I was of course meaning in the general case,
as most readers would understand.

Obviously there are cases where the efficiency calculations will be
correct, the obvious one being where the Thevnin equivalent is identical
to the original network.

If you want to make inferences about a source solely on the basis of its
Thevenin equivalent, you are on dangerous ground because you will not
always be correct.

People making the inference for example, that Zeq of a certain source
cannot be 50+j0 because the conversion efficiency of that source with a
50+j0 load is greater than 50% are wrong.

Owen