From what I remmeber reading all of the S series double down in 4 ohms. I have some info for my S/150 II which says it is also burned in for 3 days continuous into a 2 ohm load. I have a S/150 series II + a series I and the PCB boards do look different and the connection layout on the back is different and the S/150 II has a pos + neg rail fuse where as the S/150 I has a poss rail fuse and then an output speaker protection fuse which is in the signal path. the series II does not have the fuse in the signal path. Ar-t you may be getting older but your memorey is still pretty good. lol,lol
