The Fotos TM was the original hard triode produced in France during WWI.
Grammont was the company and Fotos their trade mark. When demand outstripped their capacity another lamp manufacturer, Compagnie Generale des Lamps, became involved, their trade mark was Metal and the valve TM Metal. There are differences in the construction that can help to distinguish the different makes. In particular the Fotos spherical envelope touches the base whereas the Metal made valves have a short stem before the spherical part of the glass. SeeR Type for style.
The etched design on the left is the Fotos logo and on the other side is the word Grammont. The original specification for the TM is: anode is made of nickel and is 15 mm long and 10 mm in diameter, grid made of molybdenum wire wound into a 16 mm long helix of 4.5 mm diameter. That is the grid is 0.45 of the anode diameter. The pitch of the helix is 1.3mm and there are 12 turns. The single strand tungsten filament is 0.2mm in diameter.
A closer view.
The grid is self supporting between the end connections as is the filament. The rolled sheet anode is held in three places with spot welds. The molybdenum grid is supported at both ends and each support connects to a wire in the pinch. Was the grid heated during evacuation?
The tungsten filament is held by having the support flattened, bent over and clamped. The melting point is too high for spot welding.
In this exhibit the grid diameter is 0.37 that of the anode.
An original Fotos box. Thanks to Peter den Boer (Radiomuseum.Org) for the image.
The balloon envelope is 55 mm in diameter, and excluding the B4 base pins is 88 mm tall.