This exhibit is a Sodion D-21 soft triode detector. The D-21 replaced the S-14 that was a replacement for the S-13 which itself had replaced the S-11.
The D-21 was made by the Connecticut Telephone & Electric Co. of Meriden and was the last valve designed by Dr Donle before he set-up his own company.
This soft valve made a sensitive detector but was a poor amplifier. The ions present were sodium. The filament was made of Tantalum.
The inner structure. The external copper wire is secured with twisted thread. The grid looks to be a cage of vertical strips stamped from a flat sheet.
The original box giving basic operating details.
Thanks to Joe Gruber for sending the images.
The thin glass tube envelope is 32 mm in diameter and, including the base pins, is 98 mm tall.
Reference: Joe Gruber & 1047. Type Sodion D-21 was first introduced in 1924. See also1924 adverts.
