Tube amps are divided into 2 classes, SET and class A/B
The fundamental distinction is SET/SEP and push-pull tube amplifiers. Push-pull can be class AB but also pure class A as well. SET (DHT) SEP (Pentode) are class A by default. For example, the tube push pull amplifiers I had suggested earlier are class A circuits. Granted that class AB is the more common circuit approach.
Charles