The Brimar 6K7 style of pentode was designed in the mid to late 1930s for intermediate frequency amplifiers in 'modern' superhet type receivers. It is high impedance allowing for a high Q in the tuned anode circuit.
See also the 6K7G full sized glass envelope version, and 6K7 original metal valve.
The outer cylinder is the screen. The anode cylinder is sited a couple of mm within the screen.
This example has had the metal skirt spring open.
at the base is the wire that connected the skirt to base pin 1.
The construction is a conventional pinch seal with central evacuation tube. The wires from the pinch pass through the base pins are are then soldered into place. From the top of the top cap to the base of the glass is 65 mm.
The top of the envelope: the control grid connects to the top cap. The cathode has three loops of heater within it.
The metal skirt. Inside is the remains of the cement used to hold the glass in place.
The wide glass tube envelope is 29 mm in diameter and excluding the IO base pins the valve is 72 mm long.
References: Data-sheet & 1040. Type 6K7GT was first introduced in 1938.