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 Marconi name is on the base cap.
The RVC logo.
The screening can and gettering obscures most internal details from this side.
Below the screened pentode is the screening box for the diodes. The box connects to the cathode and the individual diodes are formed from vertical rods as can be seen.
A close view.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 95 mm tall.
References: Data-sheet & 1040. Type 6B8G was first introduced in 1937. See also1937 adverts.