Quote:
Originally Posted by benman94
You've inspired me to try my hand at a Futterman style OTL. It would be nice to stop forking over so much money to Brian Sowter at Sowter Transformer...
With +60/-60 rail voltages I would feel a hell of a lot better about such a topology. The one 6AS7G amp. I'm familiar with uses +140/-140 volt rails. That makes me nervous and for good reason. It also calls for a potentially lethal hot chassis design. No power transformer, no output transformer, hell, no inductors at all! A bit scary to have something like that plugged right into the wall...
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If you swap the grid coupling caps and put them on the opposite output tube grids from the Futterman design (IIRC this was the called the Technics variant) you will have better output impedance match to low impedances. Back a few years when I was working on mine I found a site that proved it mathematically...Wish I still had the link.
OTLs are IMO the best of both worlds in amps; combining and balancing the redeeming traits of the characteristic sounds of tube and SS gear.