Where did this come from?

[hihopes]

I have a hybrid amp I am trying to understand. I would very much like to find the articles from which it was concocted, but barring that, to at least understand what is actually going on in it. It has a transistor input (ssm2210), EL34 gain stage (triode strapped) and mosfet output (10n16/10p16). Everything is pretty simply built, apart from something that looks suspiciously like a capacitance multiplier. The B+ is around 90v.

The guy who designed it is away for a couple of months, but in any case, he was always a bit cagey about where he picked up his ideas. I suspect that it is based on a combination of articles that would have appeared in the late 90’s. Can anyone direct me to where I can find information that might have been used to come up with this design? I need it for repair purposes. (Yes, I fiddled.)