The A2688 is a special quality low noise VHF amplifier triode with flying leads rather than base pins.
The anode dissipation is 2.5 Watts and the grid is of frame-grid construction. Lower noise figures were obtained by running at higher anode currents than one would expect for a small signal RF amplifier.
The A2913 is the same valve but fitted with a standard B7G base.
The GEC logo on a paper sticker.
The frame grid can be seen in the centre of the picture, the wire is much too fine to be seen.
Under the microscope the grid wire can be seen. This shot has been taken at the corner of the frame. The structure on the left is the cathode. The latter is coated only on the grid side. The U channel anode is the other side of the grid.
The grid wires seen as they pass over the frame edge.
The thin glass tube envelope is 17 mm in diameter, and excluding the B7G/F base pins is 38 mm tall.
References: Datasheet & 3002. Type A2688 was first introduced in 1959.