The goal is lofty, so I thought the best way to get there is with baby steps. Its such a massive undertaking that I'll only get one shot at this (Recording equipment parallel to Nasa's landing on the Moon). So, to make prototyping possible I plan to start small. Yesterday I built a small active tube powered splitter, which takes one signal and splits it into two outputs with independent volume controls. I couldn't do this passively without the volume knobs interacting with each other, so a single 12AU7 tube is on both channels for isolation purposes. The 12AU7 also adds some overall volume to each channel. The sound is not 100% transparent, but its very close and the subtle coloration is very pleasing. How could this be used in "The Big One?" Using this circuit (or a modification of it) I could implement several FX sends on each channel of the board. Being able to route a channel to various external effects with controls of the send volumes is absolutely critical for a Mixing board. I would be happy with 2 sends, which is exactly what this prototype box is capable of.
I really hope to create a small 4 channel tube mixer later this year. What I'd like to build is something relatively simple and rack mount friendly. I'm thinking per channel it would have volume, pan, phase invert, and low cut switches + VU meters for the stereo output. It wouldn't be cheap, but it could be priced in the realm of obtainable for project studios. It could be used to combine the outputs of 2 summing boxes or it could be used for sub-mixing, which is how I intend to use it.
This is the first post about The Big One, but I'll be writing more in the future as things develop.