The 211 is a general purpose, 100 watt, triode with a mu of 12 and maximum power to 15 MHz. It is most commonly known as the VT-4-C for WWII military applications and was used in the BC-375 transmitter. The first example is an RCA and the second a GE. They were also made with ruggedized construction by United as shown in the third example. The forth example was made by Transleteronic.
Length = 7.87" Diameter = 2.31"
Max voltage = 1250
Max current = 150
Fil voltage = 10
Fil current = 3.25