The 1636 is a UHF balanced mixer described as a beam deflection mixer. It was developed during WWII probably for Radar receivers.
The later 7360 beam deflection mixer looks to be descended from the research that generated the 1636.
The valve has a pressed glass foot rather than a pinch and is thus of modern construction and shorter leads give lower lead inductance - important for UHF.
Looking directly at the deflecting electrodes. Inside they take the form of two vertical plates.
A closer look.
The top cap connects to the multiplier dynode.
The dynode is held above the final aperture and secured at three points, the top and two side glass beads.
The wide glass tube envelope is 34 mm in diameter, and excluding the IO base pins is 103 mm tall.
Reference: Data-sheet. Type 1636 was first introduced in 1943. See also1943 adverts.