The 6AL5 / EB91 is a double signal diode. Mullard separate rectifier diodes and signal diodes in their naming convention and the EB91 would be their version of this valve 6AL5 is the American Type designation.
These double diodes were designed for sound and vision detection in 405 line televisions. Additionally they are recommended for limiting and DC restoration, again part of a TV receiver functionality.
Normally the anodes of signal diodes are left bright but in this exhibit they are blackened to better radiate heat, or maybe it was easier just use the carbonised nickel sheet for many different valves.
The twin sections with electrostatic screen in between.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 37 mm tall.
References: Data-sheet & 1040. Type 6AL5 was first introduced in 1945. See also1945 adverts.
