The B36 is an audio double triode with a 12.6 Volt heater. It is a British (M-OV) copy of the American 12SN7. This exhibit has a clear envelope and the twin triodes can be seen. The B65 is identical electrically but has a 6.3 Volt heater.
One anode face on. The grid can be seen above the bottom mica and again below the top mica.
A section in close-up. The oxide coating on the cathode is just visible. Designed for audio applications the valve has independent cathodes.
The wide glass tube envelope is 29 mm in diameter and excluding the IO base pin length, stands 73 mm high.
References: Data-sheet & 1040. Type B36 was first introduced in 1948.