Since Blackstar will not put out schematics on their products there's no clear answer for this question, but most have speculated there's some solid state pieces to the signal path. Take my HT-5 for example: it has a one 12AX7 in the pre amp and a 12BH7 in the power amp. Now I'm no expert but with only one pre amp tube I'm guessing that they designed it so that the tube is used for all the clipping, but everything else (tone stack, PI, Effects loop) are all solid state. So it's hardly an 'all tube' amp as they advertise, that said it sounds great for a basement hacking around amp so I don't care.
As far as the HT-40 goes I really don't know, maybe someone else has a better idea than I.
Amps - Marshall VM 2266, 425a, Blackstar HT-5, Galt Musical Instrument The Mason 5 (1955), Fender Blues Jr. II w/Eminence Wizard, Blackstar Artist 15, Custom 1x12 w/Celestion Vintage 30
Guitars - 2007 Gibson Les Paul Standard, 2009 Fender MIM Telecaster, 1997 Ibanez RG470