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Single Ended Triodes (SETs), the ultimate tube lovers dream.

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RE: Who makes that tube?

Posted by dave slagle on July 8, 2020 at 05:32:19:

The first picture in that article immediately actually struck my interest since the top mica support does not come in contact with the envelope. further down in the article there is a seemingly identical picture of a different tube where the top mica is in direct contact with the glass.

speculation below.... would love to see citations for or against the concept.

When early tube manufacture moved away from globe to ST shaped tubes the top mica showed up in place of a glass arbor (talking globe 50 here) This mica also was a "press fit" into the inside of the top of the tube to assure everything was visually straight. Now globe and ST 50's sound very different and the big thing you notice is when you tap the tube, the ST sounds like hitting a trash can and the globe has an almost gong like sound. When the new production globe tubes came out over a decade+ ago, the top support mica remained and tethered the top of the plate structure to the envelope. I didn't notice a major difference between globe and ST tubes of the same manufacturer. There were small differences but nothing like that of a globe vs. a ST 50. This is what made me start thinking it was not the shape of the envelope but the mechanical resonant behavior that caused the difference in sound between globe and ST tubes.

Back to the AN tube. The first picture has a screened logo and may have been a first prototype and could have used a ST mica. The second picture has what appears to be an engraved badge with serial # inside the tube and it will be interesting to see which way the final production went wrt top mica.

dave