Just finished this new amp build last week. I started with the BYOC "Brit 45" kit (Marshall JTM45 clone), but modified it to a JTM50, albeit one with a tube rectifier and a variable voltage regulator (VVR) on the power supply circuitry. You can see the VVR module mounted to the back of the chassis between the AC socket and the output impedance rotary switch; the dual-gang pot that controls the voltage levels is next to the black output jack. The VVR enables this non-MV amp to achieve tube overdrive at much more reasonable volume levels, thereby preserving my hearing and my marriage. It runs a pair of EL34 output tubes, rather than the KT66's classically used in the JTM45. At the bottom of the photos, I've posted a marked up Brit 45 schematic that shows all the modifications that were made in red.

It sounds, well, just like you'd expect a 50W Marshall to sound. I jumper the Normal and High Treble channels together and blend in the amount of treble I want with the two volume controls. It takes pedals extremely well, though you obviously have to keep the overall gain reigned in a bit when using time-shift effects (chorus, delay, reverb, etc.). The crunch tone with a Tube Screamer type overdrive is to die for.

And it's PURPLE, my favorite color!