Personally I don't care for this amps and other amps like it...basically it's a
1/2-assed attempt to have a tube in the circuit when there absolutely is no need for it. At 70 VDC is probably better than the other design I saw where the tube was powered with 24 VDC.
Thanks for the input. While the implementation is lacking, I still find it an interesting thought. I quess the question would be could this circuit be improved significantly without investing too much in transformers?
My take is that the guy was desperate to direct couple the tube to the output stage. I don't have a problem with that, per se, and in fact the tube X preamp I've been working on is direct coupled, internally. However, I think that in his zeal to eliminate the coupling cap, he pushed the rail too low on the tubes. I'd take the coupling cap and let the tube breathe properly.
And, yes, I believe this circuit has come up before, although I'll be damned if I can think of a way to coax the answer out of the search engine. Maybe the URL?
As a general note, I've yet to hear a hybrid design that actually shows the strengths of both the solid state and tube portions of the circuit. They always manage to sound decent...but not spectacular. Why that should be, I don't know. Seems as though it should be a doable thing. It'd be nice if one of our local critters here at DIY was the one to pull it off, though, as I adore tubes for some characteristics, and solid state for others.