The 6AU6 is an RF pentode for use up to 50 MHz. Bentley were a reseller not a maker. The Type designation is seen etched within an octagon on the glass - probably this was made by RCA.
The Bentley paper sticker discoloured by heat.
The anode lead is shielded to the base pin and the control grid is wound on copper supports.
The thin glass tube envelope is 18 mm in diameter and excluding the B7G base pins the valve is 46 mm tall.
References: Data-sheet & 4054. Type 6AU6 was first introduced in 1946. See also1946 adverts.