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Original Message

Well, I guess the 26 is where it all started

Posted by mhardy6647 on March 17, 2023 at 17:04:12:

See link below.
The 27 was an indirectly heated 26, it appears -- and you probably already know the story from the 27, 56, 76, through to the 6J5, and then 6SN7 (and at least as well as I). If not, you can see their entries on the same website and/or look in any tube manual(s) of the proper era(s). :)

source: https://worldradiohistory.com/BOOKSHELF-ARH/RCA-Books/RCA-Receiving-Tube-Manual-1937-RC-13-OCR.pdf