This exhibit is a replica of the French TM valve originally made by Metal (Compagnie Generale des Lamps). Like the metal valves the envelope has a short glass skirt between the base cap and the spherical bulb.
The copper base cap and simple split-pin base pins. The signature on the glass is of the maker.
The filament is a single strand held in folds of the supports - tungsten wire melting at too high a temperature to weld. The grid helix is attached to a support wire along the length. Connecting the grid to the vertical main support is a section of copper wire.
A closer view.
Face view of the nickel anode cylinder and copper grid support.
A closer view with filament wire extending outside of the support folds.
The balloon envelope is 54 mm in diameter, and excluding the B4 base pins is 98 mm tall.
References: Data, 1047 & 1003. Type TM was first introduced in 1916. See also1916 adverts.
