Re: Pre war CRT photo
In the 1980s a U.S. company successfully rebuilt a 9AP4 using the graded glass approach.
A company in the U.S. recently spent a great deal of effort trying to rebuild a 12AP4 (Pyrex) tube. They found glass for the tubing, but gave up when they couldn't find a stem that had characteristics close enough to the Pyrex. A custom stem would cost several thousand dollars in tooling cost, and a large minimum order.
For now, the prospects of rebuilding this type of tube is bleak. We are still exploring other options, though.
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