I know this is an old thread, but as I just came across 12 26HU5s (and 1 26DQ5, incidentally) I thought I'd make an observation regarding this tube. They appear to be identical in construction to a 26LW6 without the cooling fins welded to the ends of the plate, in fact you can see where the ends of the plate are folded over where the fins would be inserted on the LW6. This is just on the GE-manufactured tubes, the one Sylvania I have is identical to a small Sylvania 26LW6, fins and all. The pinout is identical as well, and the differences in the datasheet pinouts aren't there upon real-world observation. I haven't had the opportunity to fire them up yet, but I expect to see similar performance to the 26LW6, with maybe a little less max plate dissipation (compared to a small 26LW6, the big ones will eat all you can throw at it according to Tubelab. Haven't pushed the few I have but they are HUGE! Heavy too.) So... definitely some serious potential here, and probably a bass amp as well lol.