ummm, no. In order to get volume and stay clean, you need the headroom that comes from having more power. As soon as you start clipping the power tubes, you aren't really clean any more. The clean sound on a vox ac-30 isn't exactly squeaky clean, it just isn't fuzzy. Same sort of thing with the classic Fender amps.
Try to get a super clean sound out of a 5 watt amp and a 50 watt amp and see which one is louder.
edit to add:
The speaker has a lot to do with how loud it is too. The Jensens in the old fenders are more efficient and cleaner than the Celestions in a marshall cab...
All things being equal, more power = louder clean.