Oups, didn't read the first two pages of the article.
Quote:Most of the examples we will examine do not require true current-source amplifiers, only amplifiers of quite high output impedances. Most of these cases will be happy with an output impedance of approximately 47 ohms or so and prefer 47 ohms loaded in parallel with the output of a current source. That being the case, you can build a Thevenin Equivalent of such a current source by placing a large resistor (here later referred to as R0) in series with the output of a high wattage voltage source amplifier and get similar results.
Everything is there :
http://www.6moons.com/audioreviews/firstwatt/firstwatt_2.html