The De Forest DV-7 is an audio output valve with an ceramic base and was released in late 1925 or early 1926. The extended paper label was introduced in 1925.
It has a power output of around 70 mW - quite small for the heater power.
Thanks to Joe Gruber for sending the image.
The wide glass tube envelope is 32 mm in diameter and, including the UV base pins, is 105 mm tall.
Reference: Joe Gruber. Type DV-7 was first introduced in 1923.
Absolute Maximum Operating Conditions¶
Updated September 22, 2020. shape:wide.glass.tube construction:pinch type:triode age:1920.1930 base:uv heater:5.0v pins:4 pin: