The 6B8G double diode plus voltage amplifier pentode was designed for detector and first audio stages in radio receivers. The diodes would be for signal and AGC detection and the high impedance audio pentode would provide good small signal gain for feeding into an output pentode or beam tetrode such as the 6V6G.
The diodes follow the normal pattern of being placed below the amplifier section and shielded within a box connected to the cathode.
The top of the screened pentode. The control grid is taken to the top cap for maximum signal isolation.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 98 mm tall.
References: Data-sheet & 1040. Type 6B8G was first introduced in 1937. See also1937 adverts.