This relatively small cooled anode triode from STC has lost its type designation but thanks to Peter Yager it is known to be an ML-5666.
The connections are one for each end of the filament and two connections to the plate that holds the grid cage. Cooling would be by either external cooling fins or an external water jacket.
The wide metal tube envelope is 90 mm in diameter, the anode is 50 mm in diameter. Including the base pins the valve is 270 mm tall.
References: Datasheet & Peter Yager.
Absolute Maximum Operating Conditions¶
Updated April 08, 2013.