Speaking of batteries, does anyone know if the D cells and the 9V drain equally? Do I end up replacing all at once?
Based on the data sheets for the batteries, they should last about the same time, roughly 200 hours.
In the real world, it seems that batteries in perfect condition that might meet data sheet specs are pretty uncommon. I suspect @mortron has a good idea, in that AA's are so widely used, they are both cheaper per watt-hour, and probably fresher, than any other size. You can parallel a similar number, half for each tube, to get a similar-lasting filament battery. You may have to pay more for the battery holders than the Quickie though!