Figure 1 is an end view of two cylindrically constructed triode tubes. On the left is a filament type. The filament is represented by a dot at the center. Surrounding it but not touching it is a dashed circle representing the grid and surrounding that but not touching it is a solid circle representing the plate. On the right is a heater type triode. A dot at the center represents the heater. Surrounding it and touching it is a thick circle representing the insulating material between the heater and cathode. Another thick circle touches the one representing the insulator and this one is the cathode. The dot and circles are different colors so they can be distinguished from one another. A dashed circle, representing the grid, surrounds the cathode but is not touching it. A solid circle surrounds the whole thing without touching it which represents the plate. End verbal description.