The 7B6 is a double diode triode, the design use was as detector, AGC rectifier and first audio voltage amplifier in broadcast superhet receivers and effectively was the 6Q7GT on the then new B8B or Loctal base.
The printed Brimar identification. Within the triode is at the top with the diodes placed at the bottom. The locating pip is on the metal skirt in line with the locating strip on the spigot.
The actual diode anodes are short vertical rods within the outer case. The latter is connected to the cathode.
The wide glass tube envelope is 28 mm in diameter, and excluding the B8B base pins is 56 mm tall.
References: Data-sheet, 1040 & 4018. Type 7B6 was first introduced in 1940.