[1] has a collection of circuit diagrams /schematics for Fender amplifiers. The Champ circuits look very simple with basically a volume control.
[1] https://www.thetubestore.com/early-fender-guitar-amp-schemat...
Many of the early amp designs were either cribbed from radio amp or ham amp power stages--these are "clean".
"Distortion" wasn't a thing until much later. For instance, the whole reason why "fuzz" pedals came into existence is that a volume control on the preamp wasn't a common thing at that point--and were talking the mid 60's at that point.
Another musician said he'd poke holes in the speaker with a pencil. And another said the "drunk band" dropped the amplifier while loading it, damaging it, but they liked the damaged sound and kept it.
I have a 1950s Supro 5 watt (similar to a Champ) that hardly has a clean sound in it. By the time the volume is at noon, it sounds like what you imagined a wall of Marshalls sounded like when you first saw a picture. Fantastic recording amp. It's that sound, the sound of rock.
Fender was by far the most important innovator for amps, too. Most tube amps today are derived from early Fender designs like the Champ and the Twin (although they're often two or three generations removed at this point).
Of that, the loudspeaker(s) and the cabinet it's in are as important as the circuit.