This is an excellent example of the early experimental devices that Sir Ambrose Fleming had made so that he could investigate the Edison Effect. These experiments later were re-conducted with the aim of making a sensitive radio detector.
The commercial product using his ideas can be seen in Fleming.
This exibit clearly shows the base of the experiment to be a light bulb. The thin anode plate is held in place within the hairpin loop of the filament. Some evaporation of the filament has taken place as is indicated by the darkening of the bulb.