The 1B8GT is a diode, triode and output pentode for use in portable battery compact receivers. Functionally this valve incorporates the electrodes of the 1H5GT and 1T5GT in a single envelope.
To the right of the paper label the remains of the Hytron name can be seen.
The output pentode has an oval anode and can produce up to 0.21 Watts of audio. The right side has the triode at the top with the screen round the diode anode just above the lower mica.
The triode anode with the final grid winding just visible at the base. The white single strand oxide covered filament passes through the central mica and then into the diode screen. The diode anode surrounds the filament.
In this view the filament strands of both sections can be seen. There is no screen between the pentode and the other side.
The pentode seen from the base.
The pentode from the top. The central rod connects to the top of the filaments via fine spring wires.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 68 mm tall.
Reference: Datasheet. Type 1B8GT was first introduced in 1939.