NO, this isn't any secret, out-of-this-world construction. It's a way to solve the problem of having an SE-amp but just PP-transformers.
I bring this class of amplifiers to my site as I for a very short period hade built one but, as often, never tried it. The transformers are sold long time ago, anyway.
The idea is to use pushpull transformer for a single end amplifier, and hooked up in an odd way. The two output tubes are connected to one transformer and the other transformer is used to extract a summation of the signals to the two channels and then subtracted in the OP-transformer. The theory, which isn't hard to grasp can be studied in the abstracts below.