@dynacohum " I know they were supposed to have "tubelike" sound, but I can’t reconcile that with the fact they were not transformer coupled and had typical solid state low output impedance."
I was wondering about that too. Did the transfer function only work at a set volume on a specific speaker or did he actually manage to simulate the output transformer’s effect into various speaker loads and at various volumes? There’s nothing stopping anyone from putting an output transformer on a solid state amp so he could have done that, although I think that can be kind of expensive.
As a side note, Linear Tube Audio is using some method I don’t fully understand to reduce the typical effect of an output transformer on their tube amps. I’ve heard these amps at audio shows but can’t tell you much other than it sounded like it was working and making good sound with no particular sound signature that I noticed.