Were there general differences in the chemistries of metals and coatings of how tubes used to be made (that NOS stuff that people are paying $$$ for) compared to how tubes are generally made today? If the general differences between NOS and new production tubes were only down to mechanicals, it seems that new production tubes could be made more consistent with modern computer controlled machinery. And for all I know, maybe modern production tubes are made more consistent, where differences are in the chemistry. I am not saying that is the case. I'm asking the question. Has there been some major chemistry changes for audio tube components, along the lines of what happened with phasing out lead solder in manufacturing in favor of lead-free? And I wonder if anyone out there has spent time and published info on that.