Clipping diodes, and two sets of them, screams distortion to me, but we digress…
“Clean” is maybe too broad a term. That’s my fault.
If you look at DG’s Hiwatt settings during his Fuzz Face era, he’s got the Normal Channel anywhere between 1:30-2:30 with the Master at around Noon.
It may not be distorted but it’s LOUD and pushing a lot of air and with a very stout bass response.
As an amendment, I should say that I prefer FF/MK II pedals into a truly dirty amp but at the very least, you need to have some volume for them to sound their best.
In my house I have a low wattage amp. So when I say “clean”, I’m typically talking about low volume. That’s not the case for most other people, where clean is bigger and bolder.
That’s my fault and now I feel like an ass for not clarifying!