All AtmaSphere designs use what they call "Balanced Differential Design", which is quite different from the traditional Futterman approach to OTL. The heart of the circuit is a completely symmetrical output stage. This avoids the asymmetry inherent in the Futterman design and its successors. Indeed, I would say that this is even more symmetrical than a complementary transistor amp, since the output devices are identical. The basic design was originally used in the Wiggins Circlotron in the 50s.
The diagram shows the basics of the output stage. In reality, each of V1 and V2 is actually made up of eight parallel triodes (four 6AS7G tubes). Each of the power supplies (shown as B1 and B2) must be fully independent, with its own secondary winding, rectification and smoothing. This is the only real additional complexity of this configuration.
