Amplifiers are engineered from the output terminals backward. Amplifiers are always designed for a particular speaker or speakers and any amp designer who says differently is trying to sell you something he doesn't own. How the amplifier behaves into the chosen speaker load is the first point to consider when making all major engineering decisions. This amplifier was created to power Altec VOTs, Edgarhorns, WE-755As, and Altec 601As. I used a circa 1946 Altec VOT system to do the initial design work.
Output transformers are the cornerstones of any tube amplifier design.
I prefer the Tango to any other. I distributed Tango in the U.S. until 1993. An amplifier that is slew limited or unstable outside of its passband will never have good tone character. I believe the ultrasonic and infrasonic behavior of a SE amp must be carefully examined. Excessive phase shift or ringing in these regions will surely sabotage the amplifier's potential for greatness.