Hi
It is a push pull amp comprised of 4 individual SETs, 2 per channel. Class A, zero feedback of any sort. There are a couple of little tricks beside that, but that is the basic topology. The OPTs combine the two out of phase halves of each channel. Trust me it works beautifully. I am not done tweaking. The next iteration will have the custom ITs and be mono blocks because I can then fit more power supply tweaks in the boxes. But the current one is the best amp I have heard to date anywhere. Semi-retirement is fun:)