The Type 717A is known as the 'little doorknob' (for the doorknob see 703A). Intended as a low-noise front-end amplifier in UHF radar receivers, the 717A achieves 4 ma/V despite its small size. Designed by Western Electric, the 717A was made in large numbers by several US manufacturers during WWII. It was a successful valve although it was soon superseded by improved (and cheaper) all-glass types.
The US Government procurement code was VT-269 and this also appears on the metal base shell.
The Tung-Sol name.
The dome on this exhibit is fully silvered by the internal gettering.
The balloon envelope is 34 mm in diameter and, excluding the IO base pins, is 35 mm tall.