Hi Nick, welcome in 🙂
I hadn’t even heard of their Lionheart (had to look it up) but I am a valve-sniffing anal-retentive, so you’re welcome to read my ops.
Looking at the spec (I can’t find an opened-up, see the guts pic anywhere) there seems to be a lot going for it. The only cautionary point is that I think they’re pushing it a bit with the “handwired, boutique” labeling to justify a not-inconsiderable £450+ price. That phrase, to me, suggests that the major components are mounted on a turret board and wired together by a human using solder. In fact, the Lionheart uses a printed circuit board. Nothing wrong with a well-designed PCB (better than some spaghetti “handwired” amp designed by idiots) but there’s no denying that the PCB makes it vastly cheaper to manufacture.
With the parallel EL84 setup (and it really is Class A, not just biased a bit Class A-ish) it suggests to me the sound will lean more to the chimey Vox AC30 rather than dirtier Marshall territory. Some alternatives worth considering before you commit to the Lionheart. The Vox AC30CC1 costs about the same as the L20H and comes with a very decent 12″ speaker. The CC2, with 2×12″s, is only slightly more. Laney’s matching 2×12″ cab, don’t forget, pushes the whole Laney price towards £900. This puts it against the Marshall 18W RI, which is a lot more basic than the Laney (it sticks closely to the 1974x original) but the Marshall is a true handwire.
The Marshall is also more of a cathode-biased push-pull design – hence it can make 18W out of just two EL84s whereas the Laney’s 20W requires four. The Marshall will “crunch” more as it’s dialled up. I have several WEM Dominators (the design that Marshall pinched wholesale) and I do like their “ministack” sound; even from a single 12″.
There’s another suggestion to try before deciding and that’s the Orange Rocker 30. I like the idea of the “vol control only” clean channel and, as it uses 2xEL34 valves, it should be good for that bigger-Brit amp sound. £615 but, again, it’s a combo with a decent 12″ speaker. If you go for the 20H, the matching 212T cab is worth trying. I think a 4×12″ is overkill with that sort of output.
Just a few ideas. Wait for Lee_UK to pitch in with his ops. He knows a lot more than I about the merits of various speaker drivers for guitar and is very well versed in AC30s. Hope some of this is useful 🙂