The EF184 is a purpose designed high gain frame grid pentode. The EF184 superseded the ubiquitous EF80. The mutual conductance is 15.6 and the closely related (pin compatible) variable μ pentode EF183 has a μ of 12.5.
In 1969 the EF184 was described: a frame-grid sharp cut-off pentode for use as an IF amplifier in television receivers. This implies a relatively wide band function at about 33 MHz. The high mutual conductance was important for wide band width amplifiers. Mullard quote operation at 40 MHz for their version.
Within the screen can be seen the strap that connects the two small plates of the anode together.
Compare with the image abode: the lower bright plate with the right angle section shields the anode and screen grid.
The thin glass tube envelope is 20 mm in diameter and excluding B9A base pins, is 53 mm long. The electrode assembly is 13 mm top to bottom.
References: Data-sheet, 3002 & 1040. Type EF184 was first introduced in 1960.