The 6F28 is an amplifier beam tetrode of high mutual conductance designed for television service and introduced by Thorn-AEI (Mazda) in 1961. It is also known as the EE80.
R J Sutherland points out that the tetrode section of the 30FL12 has identical electrical characteristics to the 6F28.
It was designed for use as a video output valve where the high mutual conductance makes it easier to achieve a reasonable stage gain and wide bandwidth.
The perforated screen hides most of the inner details. There are screens above and below the mica discs.
Made in England and the BVA identification.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 47 mm tall.
Reference: 1040. Type 6F28 was first introduced in 1961. See also1961 adverts.