12x12 ought to be plenty. Remember, I have twice as many things, and most of them are bigger. The amplifier section is made up of 6 valves, 2x 12B4A and 4x 12BY7A for the active loads. The first one of these I built on 5 3/4 x 11. I am going to resurrect it with 12B4's and the rest of the Guinevere circuit. I was goig to use 6 1/4" but the milling machine vise only could take a 6", so I trimmed it so I could clamp in in the vise.
regards,
Douglas