Didn’t the Wired piece say "Blackburn"? That’s Mullard territory. Somewhere on the web is a very long set of pieces about Mullard back in the day. It is fascinating and almost steampunk like the movie "Brazil." Rube Goldberg stuff that was mechanized but not computerized. Well worth watching for the fun of it.
If they took Mullard tube making equipment, and plan on making that tube with more modern techniques and materials, my bet is that it is still warm. That isn’t to say it isn’t worth buying. I only use one pair of 12AX7 ( the old ARC SP 3 was filled with them) and prefer a ribbed plate Tele, old, it gives a degree of "roughness" to what would otherwise be too sweet. Have I rolled every tube? Nope. And I have a particular application of specific gear that is voiced as a system. Results may vary. But the 12aX7 (WE never used to make one, right?) is a ubiquitous tube, common in great older audio circuits and finding true NiB/NoS is a luxe good now.
The 6h30 is a maddening tube. I’m running a late 70s quad matched set that was never used until installed a couple years ago. Replacements of the DR Refl. tube from early production range from counterfeit to impossibly expensive. Very frustrating tube to own. (Some people claim that listening to modern reproductions out of Russia make no difference- maybe it is the circuit. It’s pretty obvious- dead v. air, dynamics and punch.
I wish them the best-
Tubes are just another layer of PITA that makes this sick hobby fun. I’ve been doing tubes for almost 50 years and consider myself a babe in the woods. It’s deep, dark and dangerous.