Thanks for generously sharing your schematics and ideas. I was inspired to build this amp because of quality of your work.
I built the amp using premium components and it is, without a doubt, the best sounding amp I've ever played. The cleans on it are buttery and bluesy, and the bass freqs are tight. On the low voltage (420v) setting, it starts to break up at Vol 4, and if I jumper the channels it becomes a rock monster.
I prefer the 420v setting to the 690v, as I don't need the additional headroom for my usual style of playing. When I want to play jazz with an arch top, I'll switch to 690v which seems to add a bit more space to the tone. Tubes are Winged =C= EL34s with JJ 12AX7s. I tested Mullards, Groove Tubes and Tung-Sols on the pres, and found the JJs sound the best. I mainly play Strats with vintage-spec pickups, with mostly clean tones at the edge of break up. This amp seems custom-made for this style.
In my earlier posts I was trying to sort out how to tune the voltages, and ended up using a 22K drop resistor in place of the 8.2K. That brought my plate voltages close to spec on both settings. I also used separate bias pots, so I was able to dial in for both voltage settings.
I used a steel Ceriatone chassis and had no noise issues with the tranny locations. Like you, I'm a believer in the Larry Ground technique, and find it works so well I no longer shield the input leads.
For transformers, I went with ClassicTone's 50W Drake replica offering. I haven't used their iron before, and the low price worried me a little, but they really deliver. http://www.classictone.net/Marshall-Style-Transformers.html#anchor_1199
Their PT is wired for high/low voltage, which is why I decided to figure out how to wire both into the circuit through a switch.
Peter Mather in Nashville http://www.mathercab.com/price_list_marshall.htm
built me a great BB 2x12 cab (his cabinet work is the best IMO). I spoke to Jim Seavall at Scumback about the amp and he recommended 65-watt M75 and H55 speakers, which sound great in this application. http://www.scumbackspeakers.com/m_series.html
By going with the 65-watters I can also plug a 100-watt head into the cab later if I want to. (I'm now building a JTM45/100 head)
I'll post some pics soon. Again, Scott, I want to express my gratitude to you for sharing your research and best practices with hobby builders like me. It's great to be able to build something this good, and that would not be possible without folks like you.
PS - I caught the OT wiring mistake you mentioned ... the old fashioned way. It was midnight, of course, and the foghorn blast awakened my entire household.
I see you added an FX loop to your schematic. How is that working? Any noise issues with it?