The 6K8G is the classic triode hexode frequency changer or mixer for broadcast receivers. The exhibit has a clear glass bulb and would rely on external shielding where other mixers had external zinc paint sprayed on to provide screening. For isolation of the signal input and output circuits the hexode signal grid is taken to the top cap.
Etched into the glass near the base is the word Canada indication the Country of Origin.
A diagram of the construction can be found in 6K8.
The outer screen. The hexode anode is fixed to the lower mica and can be seen on the left of the image. The heater, cathode and inner grid can just be seen on the right.
The hexode electron flow is from right to left in this image and the triode anode is on the right. The bright plate in the centre is an internal screen.
The triode anode inside the screen. Outside the lower mica is the rectangular cathode etc.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 97 mm tall.
References: Datasheet & 1040. Type 6K8G was first introduced in 1938.