Balanced SET? North Audio

Sounds like push-pull to me. Or maybe bridged. A gimmick IMHO.

When stereo was new there was a brief interest in converting mono amps to stereo, without adding any output tubes or power supply. (Yes really). My memory of the circuit details is a bit dim, but it involved connecting the center tap of the output transformer through the primary of another transformer. One channel drove the output tubes in common mode, and came out of the auxillary transformer. The other signal drove the output tubes differentially, and came out of the original transformer. The signals involved might have been L+R and L-R instead of L and R. Certainly the rig would work better with the relatively small A-B being the common mode signal.

Anyway, such an amp might be described as push-pull and single-ended at the same time!!