Type 6BR7, like the Mullard EF86, was carefully designed for low internal noise and, especially, for low internal hum pick-up from the 6.3V AC heater, thus making it unnecessary to provide a DC source of heater current.
These features made these valves the standard 1960s choice for the input stage of sensitive hi-fi systems, displacing type EF37A which was the previous (British) favourite for this application.
The screening is extensive and just a glimpse of the wire grids is afforded by the notch in the screen. The anode is hidden behind the screen to the left and right.
The heater is wound as a double helix.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 47 mm tall.
References: 1040 & data-sheet.