Kora Class A audio amplifiers are powered by SquareTube, a tube/transistor design that is not a traditional tube gain stage combined with a transistor power section, but a fully hybrid system that simultaneously uses vacuum tubes and transistors. In essence, the tubes provide the signal voltage (the actual music signal) while the transistors provide the current (the power). Whereas Kora’s more modest amplifiers are Class A/B designs, the big Class-A amplifiers combine SquareTube with pure Class A transistor power from a highly filtered linear power supply.