The 6AL5 is a double signal diode. These double diodes were designed for sound and vision detection in 405 line television receivers. Additionally they are recommended for limiting and DC restoration, again part of a TV receiver functionality.
This exhibit was made by RCA at their Brazil subsidiary.
The bright anode is stitched together.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 40 mm tall.
References: Data-sheet & 1040. Type 6AL5 was first introduced in 1945.