The 6870 is described by Brimar as 'Trustworthy' presumably this denotes a special quality valve.
The design purpose of this high slope valve is RF power or video amplification. The first date reference we have is 1959. The valve was not listed in 1953.
The anode is blackened to assist radiating the heat generated when operating, this can be as much as 6 Watts.
A closer view reveals a true pentode with three wire grids.
The grids are wound on copper supports.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 60 mm tall.
References: Data-sheet, 4053 & 4004. Type 6870 was first introduced in 1959. See also1959 adverts.
