I’ve got a question for the power-crazy folks among us, who use power trafos for OPTs. Or perhaps someone just stuck up against impedance flexibility. First a little background and the motivation here. The ultimate goal is building a “1000 watt” (per channel!) amp using 26LW6 tubes driving Antek 15T950’s as OPTs, which is in the process of gathering the parts and working out details. If it takes 15 years I don’t care. At the moment, I’m doing the “intermediate” step of building one a little smaller but the same general idea. Using up to 8 21LG6’s to drive an Antek 8T800. The best configuration is to use 600 V B+ (under load) with 8 ohms load, and should give almost 350 watts. The speakers won’t always be 8 ohms - that pair hasn’t even been constructed yet - it’s on the to do list and waiting on a recone kit to boot. The BIG one will only be used with 4 ohms so impedance flexibility is not an issue. But impedance flexibility would be nice here. So what to do with a fixed Z OPT? My thought is to lower B+ to 450 for 4 ohm use. Are there any gotchas that make this impractical? Different optimum screen voltage, but that will come from a regulator anyway and could be made switchable. Sweep tubes have enough current capability on paper anyway. How likely would it be to need rebalancing of the bias (to keep DC out of the core) when changing the B+, or will one adjustment for the group be enough once it’s initially trimmed?Has anyone done this? I already have the power trafo solution on hand for “8 ohm only” operation, but have a couple identical of donor cores that I could wind up with the proper taps to provide both B+’s AND the lower screen voltage for the regulator. Is it worth making these power trafos (would need to buy a roll of wire of the proper gauge so all the winding fits - I’m not sure a #19 will fit and 22 is undersized). Or is it a fools errand and should just use what I have on hand for and design for 8 ohms only? I will during initial phases.