Thorne; Like Dave said, the 1n5408's are fine for the KX-200. Both the 1n5408 and the STTH3R06RL are rated for 3A with the 5408 voltage being 1000V. I've used 5406's in one or two units (600V piv) in the past, but it's really not enough headroom, due to surge voltages, especially if Filter capacitance is raised. I like a 150% safe area above the highest voltage spec'ed from the transfomer for Diodes. For example, say your highest B+ is 525V. 150% is 787.5V. Therefore a 1000V would have the headroom, but a 600v could possibly be blown from overvoltage upon turn-on(especially if the amperage is at or above rating). Luckily FISHER's gear usually doesn't draw more than 2.5A on turn on (at least none of them that I have seen) so there may be some fudge room. For now I stock just the 5408 and 4007 (1000V) for rectumfriers, and the 8A table bridges.