The simplest usable tone stack is a single Tone control: one variable network that rolls treble off the signal. There is no separate bass or middle control and no cathode follower to drive — just one knob between a dark setting and a bright one.
This is the small- and medium-tweed answer — the Deluxe, Harvard, and Princeton — where one control was enough and every part counted. It shapes the amp's inherent midrange voice rather than carving three bands out of it, which is much of why these circuits sound the way they do: forward and vocal, with tone set by feel rather than by a full stack.
It sits one step up from the amps with no tone control at all and well short of the two- and three-knob stacks the larger amps carry — the middle rung of the archive's tone-shaping ladder.