I have a Futterman Harvard Music H3a. Mine is a bit different than the photo here. Just a pair of HB5 pentodes connected to an Altec autoformer per channel. This was a special order to drive a low impedance speaker system. I bought it from the original owner who used it in the 60’s.
The Futterman OTL is NOT a circlotron! It is a totem - pole arrangement with one half of the output stage as a cathode follower and the other half having unity gain. Julius used 60db of feedback to reduce distortion and lower output impedance to make his circuit work with 8 ohm speakers.