The DE11 was the first Cosmos dull emitter valve and was introduced in 1924 as a general purpose triode. At the time Metro-Vick claimed that operating the filament at 1.1 Volts and 0.25 Amps required a thicker filament and thus was less fragile.
The etched lettering includes the Cosmos trade name and the Metro-Vick logo. The filament rating is present as is the Type designation. Below is the type 3 BBC stamp, thus dating this valve to between September 1924 and the end of 1927.
The gettering hides all of the internal structure.
Thanks to Graham Vine for donating this exhibit.
The wide glass tube envelope is 26 mm in diameter, and excluding the B4 base pins is 79 mm tall.
References: 1004 & 1003. Type DE11 was first introduced in 1924.