The 6F26 is a VHF varible-mu pentode where the stage gain is controlled by the negative bias applied to the control grid. At the time this design was developed television receivers operated on Band I at about 50 MHz and from 1955 also on Band III at around 175 MHz. The EF183, released in the 1960s, overtook its performance.
When Band IV and Band V UHF television entered service in the early to mid 1960's the front end required specialised triodes to operate at 400 - 850 MHz.
The reverse side of the circular anode and the made in England by a BVA member.
The compound pins with the red section having the same expansion co-efficient as the hard glass used for the base.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 59 mm tall.
Reference: Datasheet. Type 6F26 was first introduced in 1960.