the Tung Sol 7236 are pretty nice if you can't find tung sol 5998, these tubes are kinda hard to find, so this wouldn't be a bad buy.
the best by far for the HD 800 though are the GEC 6AS7G, most transparent, sweet beautiful tube sound (Even better than 5998 which is already quite impressive), great textured tight bass, and very detailed treble and mids, lots of air. it can be a little bright at first, but after the tubes are fully warmed up, they sound amazing.
the Westinghouse 6V4 option jack sells is a total ripoff. look for a mullard ez80 or RFT EZ80 (these are easily found for $25 a pair NOS).
i wouldn't pay 290$ for amperex 7308 either, though i'm sure they're decent tubes.
amprex 6dj8 bugle boys or some of the nicer amperex tubes are good for HD 800. im sure the siemens tubes are pretty good too. and my old favorite the jan sylvania 7308 is pretty good too, a little darker, but nice.
Edited by Dubstep Girl - 8/6/13 at 8:59pm