With the FQH44N10 in Q1 I tried the IRFP 140 and FQH44N10 in Q2 and preferred the FQH as it sounded fuller with better bass.As noted above, the IRFP150s have a higher gate capacitance (and gate charge) than is typically used in the ACA. Nonetheless, they can make very good current sources in the Q2 position on the ACA board. Several intrepid amp builders have tried the FQH44N10 in the Q1 position, quite recently in fact, and have loved the results. That would be my best recommendation.
Thanks again, I will do some reading etc... I would lobe to copy the one you made!Yes, the single-rail SLB is what I used in the external PSU for my VFET amp. It needs a transformer with 30V secondary voltage in order to produce an output voltage of 36V. Two 15V windings in series work well.
I also used the dual-rail SLB in my F6. I have built my own capacitance multiplier supplies without the aid of a PCB, so I was already familiar with the circuit. The SLB uses a complementary feedback pair (aka Szklai) for the high gain pass element. It is nice to have these PCBs available to make the job easier. The LT4320 rectifiers seem to work well at reducing the voltage loss due to rectification.