Every time someone brings up this topic, I order more tubes, it gives me anxiety. Jokes aside, I think the tube market is pretty healthy for now, and it is mostly thanks to us guitarists. I think they'll be around for as long as we are. I stockpile them nonetheless, and not necessarily NOS tubes. In terms of quality, I think the current production tubes are very good and that's what I tend to stock. I have NOS Brimars, Mullards, RFTs, Sylvania and lots of NOS Soviet tubes I got for cheap back in the day. But what I buy the most are cheap Shuguangs and JJ's. I use them in builds and repairs, and I've never had one fail on me for years. But I've had expensive NOS tubes fail on me. New production tubes coming out of China are more rugged, they have thicker glass, more mica holding everything in place which makes them less microphonic, no filament flash, they can take more punishment and they sound very nice to my ears. Back in the day, tubes were made for all kinds of applications, but these days they are made only for audio, and guitar amps in particular. A tube guitar amp is a very hostile environment for tubes, and companies understand that and base their specs on those well known failure points. It's not just tubes, I think new transformers form Canada and Europe are good too and so are the capacitors. I buy lots components, I think this is the golden age of electrical components of all kinds. Modern manufacturing technologies means old components can be made cheaper and with higher quality. But don't take my word for it, I'm just a hack.