The AG8 is an octode mixer or frequency changer for superhet receivers. The Cossor designation would be OM8
The local oscillator would be formed by using a grid one as the control grid and grid two as the oscillator anode. Grids three and five are screen grids. Grid four is the signal input grid and grid six is the suppressor grid.
The cathode and grids 1 to 5 are in a line with both rods of grid two strapped together, grids three and five are also joined at the top. The grid 6 supports are at right angles to the main axis.
No details on the AG8 have been found other than its equivalents. In The Radio Constructor for March 1962 a dealer does list the AG8. Harverson's price was 10/6, an AC/Pen was 23/3 and a KT66 was 12/6 - how times change.
The reverse is plain with the wire connection to the screening paint clearly visible under the round sticker.
The round cathode in the centre with hairpin heater within and the grids radiating out. At right angles to the main grid line can be seen the support for the suppressor grid. Grid two is a pair of un-notched rods joined at the top, these form the oscillator anode.
The classic envelope is 28 mm in diameter and, excluding the IO base pins, is 78 mm tall.
References: Data-sheet, 1040 & 1043. Type AG8 was first introduced in 1940.