EMI Pyrex CRTs

[ppppenguin]

My understanding is that all the prewar EMI tubes were Pyrex borosilicate glass. Certainly the one that I had rebuilt in 1986/7 was borosilicate . Charlie Bradley, the guy who did much of the rebuilding work, had worked on these tubes when they were new. He did a graded seal to match the tempco of borosilicate to the soft glass pinch that he used in the rebuild.

Borosilicate tubes used tungsten wire in the pinches which gave a decent tempco match to the glass. Soft glass pinches used a very different alloy.

Here's Charlie with the actual 6/6 I had rebuilt, part way through the job.
http://www.borinsky.plus.com/ptv_crt_regun/2.jpg

This article strongly suggests that as far as we are concerned for CRTs Pyrex= borosilicate. https://en.wikipedia.org/wiki/Pyrex

Overall I'm not convinced that those numbers are tempcos.