> Those parts that everyone thought were dirt cheep, so people stopped making enough of them. Not only that, but because (in this analogy) tube making machines

> Those parts that everyone thought were dirt cheep, so people stopped making enough of them. Not only that, but because (in this analogy) tube making machines are very expensive, low-volume machines made by only a couple of companies in the world, take a long time to make, make only single very specific kind of tube each and take a long time to install and commission, you can't just up and start making more tubes. And on top of that, the machines cost so much and tube technology moves along so that if you're not careful, you may never turn a profit on the tubes at all if, by the time you're tooled up, you've missed the window of opportunity and no one wants that many old-style tubes anyway.