This is the very common Mark Houston circuit on the net a supposedly 5w output using a 2SK1058 (Spice parameters correct). But it is nowhere near 5w, in fact it has gain reduction (but works). The 15 ohm resistor handles all the current taken by the FET so it needs to be 20w. I am putting CD Player voltage at the input but the output would not reach 5watts even if you put 10v signal in the input. Something is wrong - People have built this circuit and found the output to be OK.
I'm confused? The peak output could be as much as 4.5w because of the voltage swing but on the simulator it is not even 0.5 w.
