Type VT-217 is the US Government code for the commercial 811. The valve is an HF/VHF transmitting triode rated for operation up to 60 MHz and at one time widely used in military and professional applications at frequencies which other HF types cannot quite reach.
The VT-217 (811) was popular valve on the War Surplus market during the late 1940s and early 1950s.
The data given is for Class C operation. The control grid current can be up to 35 mA. The overall rating is high for a valve of this size but, slightly derated, very suitable for amateur use in the higher frequency bands.
The anode from the side.
The envelope carries the commercial 811 etched into the glass and the base cap carries the full information.
A closer look showing the control grid and four strands of filament within.
The top mica with filament tension springs and anode connection to the top cap.
The classic envelope is 60 mm in diameter and, excluding the UX4 base pins, is 148 mm tall.