i've only tried mine (JCA50H), but mine has absolutely tons of gain. Like... i run the gain at 3 on the overdrive channel (granted i use a boost, a danelectro timmy clone- but before i tried it with the boost i had the gain about 5, it's not like it needs the boost, just i'm so used to using a boost now that i prefer it). The normal channel has enough gain for hard rock/80s metal, lol, let alone the overdrive channel.
the only thing i'd say it, it's not a totally modern type of tone- it's tons of gain, but in a late 80s type of way. But yeah, tons of distortion in there unless there's something wrong with mine.
EDIT: yeah as dmoney says you need to make sure you get the models which are high gain, but as long as you do, it should have enough gain/distortion. Obviously i can't say for sure, but it has enough for me, anyway.
EDIT #2: ^ i don't think the series ones have "loads of solid state stuff" like the HT series does- it's like one transistor or something. But even one means it's not "all-tube". Plus as i said, I haven't seen a schematic, I only heard it in passing from someone on some forum who said he'd seen the schematic and that, while it was a lot more tube than the HT series, it wasn't technically "all-tube" either.
I'm not sure Blackstar has ever described the HT series as "all-tube". However, they strongly imply it is (and iirc there was an official youtube video from blackstar where one of their workers described the ht5 as "all-tube"), they don't correct guitar mags when they review them and say they're all-tube, they say the ht5 is based on their pedals, and their pedals have "pure tube" plastered all over them.
They don't actually flat out say it (that youtube vid notwithstanding), but they strongly imply it to the extent that, in my opinion anyway, they might as well be.
FWIW I agree with you regarding the solid state stuff- it's actually the "right" way to build a hybrid (rather than that valvestate nonsense with like one miserly preamp tube), and the irony is that had they been a bit more upfront about how the thing was designed and made, the forums would probably have been singing their praises. But they didn't so we aren't. :lol: