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The Fotos TM was the original hard triode produced in France during WWI. 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 as can be seen here.

We also have a repaired example of the TM-Metal.

This is the original shipping container used by Metal for their TM valves. Today this is a very rare object.

Thanks to Joe Gruber for sending the images.

The balloon envelope is 55 mm in diameter, and excluding the B4 base pins is 88 mm tall.

References: Data, ¹⁰⁴⁷ & ¹⁰⁰³. Type TM-Metal was first introduced in 1916. See also 1916 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶