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20.

 
See also:
The American Shaw Radio Tube Base
    
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This exhibit is a De Forest Moorhead type 20 to avoid confusion with the later Type 20 we have used 20. in the index. This type of valve was advertised as early as 1920.
The base appears to be to the Shaw pattern.
See also 20 for more images of the construction.
Thanks to Joe Gruber for sending the image.
The wide glass tube envelope is 29 mm in diameter and, including the base pins, is 79 mm tall.
Reference: Joe Gruber. Type 20. was first introduced in 1920.

 

Updated September 22, 2020.
shape:wide.glass.tube construction:pinch type:triode age:1920.1930 base: pins:4 pin:
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