It's a clone of the "Dickinson amp" (serial number 7206), thought to have belonged to Hendrix and which Marshall used as the basis for their 100JH reissue a few years back. The circuit is basically a stock JTM 45/100 - "version 3B" according to Roe Fremstedal's excellent history of the Marshall Super Lead - with a later tonestack (33k/500pf), 10k dropping resistors and extra preamp filtering. There's some debate about when these changes occurred, as the amp didn't surface until the early 2000s.
I used Marstran/Heyboer transformers and, as you can see, quite a few NOS parts. Shipping everything over here was a quest in its own right.
After a fair bit of experimenting, I ended up with GECs for the power tubes, Mullards in V1+2 and a Valvo in V3.
The stock HT for these amps is very high (~560V). The reproduction PT had a lower voltage tap (490V), but curiosity got the better of me and I discovered I preferred the original voltage (so much punch!) After blowing a JJ - supposedly the most rugged current production KT66s - I realized I'd have to fork out for the original GECs....
Most importantly, the amp is a powerhouse. Incredible rock tone. It's obviously loud as anything, but in practice, I run it into a Boss Tube Amp Expander, which then feeds a 2x12 cab with Pulsonic T1281s.
I have a headbox - built by Sourmash in the US - but still need to cut the holes to install the correct Vox vents. As it is, running the amp outside a cabinet keeps it cool, and lets me keep an eye on the tubes!
I've laid the vents themselves on top here so you can get an idea.
