The VT-191 is the US Government procurement code for the 316A UHF power output triode, designed by Western Electric.
It is a wonderful doorknob shape, and is a famous type of valve in that it was used for the first successful radar transmitter to be operated whilst airborne. In this application it was operated in pulse mode and the individual pulses were of a few hundred watts.
The maximum grid current for its native Class C mode of operation is 12 mA.
This exhibit came in a box dated 1944 and intended for the US Army and US Navy.
The triode section is small compared to the glass envelope.
Looking through the glass the vertical rods of the cage grid can be seen.
The thoriated tungsten filament connects to a pin below and at the top the connection is via a tension spring.
The balloon envelope is 60 mm in diameter and, excluding the special base pins, is 60 mm tall.