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The SL2-787 is a directly heated triode transmitting valve. The support structure is stout wire that is brought out through glass metal seals. The connections are to copper braid that is bonded to the connections.

The filament is supported on metal plates. These are squares that have had the corners cut out to form a cross. The filament is threaded around the cross and passes eight times through the anode cavity. The grid is a wire helix held on rod supports from a cylindrical fixing. In our specimen the anode cavity is displaced from its required position of equi-distant from the grid. Probably the valve has received a heavy knock.

The silica tube envelope is 85 mm in diameter and, from tip to tip, is 312 mm tall.

Reference: Observation.