Just finished this off this morning, its a modified Vox AC15 top boost preamp/tone stack into an el84 single ended power amp. I have a build thread here: http://www.tdpri.com/threads/first-build-and-something-a-bit-different-take-2.873969/ but here's the details in brief. The original AC15 top boost has 3 triode gain stages in the preamp but 12ax7s are dual triodes so I swapped out the first gain stage for a depletion mosfet (LND150) then followed with a 12ax7 so its like pushing a valve amp with a clean boost. The knobs are volume (gain), treble and bass, 2 switches on/off and a tone stack bypass. I'm probably going to add an attenuator and maybe a switch to add more bass/mids to give it more of a Bassman/Marshall tone. I'm planning to build an enclosure for the head and I'm hoping to adapt the cab underneath for a bigger speaker (10").