The tubes that are currently still produced (mostly late designs for audio use) have never been particularly rare, at least until very recently. I'm pretty sur

The tubes that are currently still produced (mostly late designs for audio use) have never been particularly rare, at least until very recently. I'm pretty sure the 12AX7 has never gone out of production completely worldwide. There's several manufacturers; one in China, one in Slovakia, and one in Russia, at least. As the article notes the fact that a lot of tubes come from Russia is causing a bit of a price spike now. But in general, since the transistors took over, they've been available for about $10 in current dollars, only a little more expensive than they were back in the 1960s. US manufacturing faded out in the 80s, but tubes were manufactured elsewhere commonly into the 90s. It's apparently still profitable to manufacture them for $10 or so, at least with legacy tube-making equipment. The real expensive ones are like binned semiconductor parts. The best frequency response, least micro-vibrations, etc. Or manually selected pairs with similar properties. But if you just want to replace the pre-amp and don't care much they were like $12 just a couple years ago. So I don't know what the collectors are doing, really. Not exactly a market you can corner so long as people keep burning out their tubes and multiple companies keep making them.