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The Fotos Bi-Grille is a bi-grid valve from the 1920's. The French Fotos company produced some of the earliest hard vacuum valves.

See also Bi-Grille with an ungettered blue glass envelope.

The special five pin base is larger than the standard B5 base. The anode is the centre pin, with pins 1 & 2 as the grids.

The electrode system is mounted horizontally above the pinch. The filament is a single strand and the grids are concentric helix's.

The right hand side of this image shows the inner grid and the start of the outer grid helix.

The right hand side of this enhanced image shows the inner grid and the start of the outer grid helix slightly clearer.

The wide glass tube envelope is 39 mm in diameter, and excluding the special base pins is 89 mm tall.

Reference: ³⁰⁰². Type Bi-Grille was first introduced in 1925. See also 1925 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶