Working on this for a friend. It's part using spare parts to save $$$, and part making a practical amp for gigging. The transformer selection (272DX and 1750E) as well as the power tubes (6973) are simply because I have them already. So why not. This forces me to use a 5Y3 rectifier to not kill the tubes, it's okay, I have one that I don't need. I wanted to give him a nice pedal platform amp, and a cathode-biased Blackface has a nice syrupy warmth and just enough headroom for small club IMHO (the bones of it are based on one of my own ams). So then... I took this a step further. Why not put a "distortion pedal" right in the amp? With a tube, running on proper high voltage. So I added the first two stage of a Marshall SL5 for good measure, and gave it its own Tone control (at maximum it's effectively the stock circuit, but at least you can tame it down if necessary). In itself it might not create that much distortion, but it's also hitting the Blackface front end harder. Some tweaking will be required to get it where I want. This is a first draft. And since some effects work better post distortion, why not add in a loop? The Blackface architecture makes it possible to just add a buffer after the tone stack and use the 2nd triode as the recovery stage. Experience tells me it's still possible to drive the power amp hard since we're not losing signal mixing 2 channels together. Purists will not agree of course. A few quirks you'll notice: - Dual inputs: will work perfectly using just the Drive/Combo input, but if you want to leave your Tubescreamer on all the time into the Distortion side, dual input lets you do that! Or leave chorus on on the clean side only. - Relays are fed from a regulated 5VDC supply obtained from the 6.3VAC filament line (Hoffman inspired) - The rectified 6.3VAC is also used to feed DC to the filaments of the Distortion tube, using a dropping resistor (too short on voltage to risk a 6V regulator) - The loop is basically just a MOSFET follower used as a buffer after the tone stack. Exact value of the voltage divider after it will have to be tweaked. From experience, the tube recovery stage following it should have enough gain to drive the PI.