Some amps carry no tone stack whatsoever: there is no Tone knob, and the frequency response is fixed entirely by the circuit's component values and the speaker. The only controls are volume and, on the guitar, whatever the player brings.
That is the Champ-class recipe — the smallest, cheapest circuits, single-ended and stripped to essentials. Having nothing to set became a virtue in the studio: there is no tone control to get wrong, so the amp always sounds like itself, and engineers shape it at the guitar and in the mix instead.
It is the bottom rung of the archive's tone ladder — from here the circuits add a single tone control, then two- and three-knob stacks. The absence is itself the design.