The STC is an interesting design. The purpose is add 100% voltage feedback through a triode, with the idea that the amplifier will show triode characteristics, independant of type of power device.
The simplest version of this kind of amplifier is based around the ECL82, a cheap and common available tube. Also there are several choices of CCS - transistor, fet or pentode. After fiddling wwith fets, I did go for the cathode.
Simple design and well sounding amp. The big question is: are the diodes to the screen grids really needed?