The ECL86 was one of the last triode plus output pentode valves designed and was released to the market in 1962 here we have the UK Government procurement identification.
The triode on the right has additional screening around the top of the control grid supports. Screening for the triode can also be seen below the lower mica.
The screen continues between the sections and above the top mica.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 68 mm tall.
References: Data-sheet & 1040. Type CV8297 was first introduced in 1961. See also1961 adverts.