Surely the distortion could be related to the guitar.
Although I have a variety of them, they do tend to be hotter output than normal, as I've replaced the stock pickups with a variety of after market ones.
Still, when I use them with my other amps, I don't get undue overdriving of the input tube.
I've tried a few too, since the early 70s
My champ build is using not so great output transformer, tho' I've tried a couple of different ones.
And it is not really a completely faithful clone or anything. Pretty close but no clone.
However, the circuit is pretty simple!
The main thing is that the bottom end breaks apart pretty quickly when the volume knob is up - and I mostly have it most of the way up - a single ended 6V6 is probably only 3W or so. Mind you, if you switch out the tone stack it can push that 6V6 hard and get pretty darn loud.
As previously said, clean champ tones are all about the output transformer (and speaker!)
It's all good! Just saying the Champ wouldn't be my first choice for clean tones is all.