The A2975 is a planar triode for use as an oscillator at up to 1 GHZ.
The details given for the A2975 are those of the A1714 which it can replace with improved performance.
The disc on the right is connected to the cathode but appears to be a shield. The insulated heater can be seen entering the base of the rectangular cathode tube. The grid is of frame grid construction and placed very close to both cathode and anode. The anode being the large structure on the left.
In this image the disc connected to the cathode is seen through the frame grid. The wire is so fine that it can not be seen.
This is the valve mounted as close as possible to the macro lens on the Nikon DF. The image has been reduced in size.
This is a crop of the above image at full resolution. The frame grid can now be seen. What an amazing production the frame-grid was.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 45 mm tall.