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 maker's identification. The spigot and location pip are clear to see.
The internal coating restricts viewing the internal structures beyond the presence of the lower screening box housing the diode anodes.
The wide glass tube envelope is 29 mm in diameter, and excluding the B8B base pins is 57 mm tall.
References: Data-sheet, 1040 & 4018. Type 7B6 was first introduced in 1940. See also1940 adverts.
