Bombaywalla,
If setting sais @0, it doesn't mean that the negative feedback is 0.
Without one, I doubt that any full range amp is produced. The differential input stages(usually dual triode connected as such) imply the stage with 0 gain and 100% negative feedback. The output stage may than be a feedback free... again, with some degree of sacrifice to load capabilities. With tube OTLs it's simply impossible.