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This exhibit has the etched marking of 4 in a circle but is a 1920s R Type bright emitter derivative.

The filament is a single strand and the electrodes are co-axial within the cylindrical anode. The grid diameter is smaller than the R Type.

The strap across the grid adds extra rigidity.

Just below the anode the filament voltage is etched and reads 4V-0.7A.

The electrodes seen close-up. The tungsten filament is held in place by being crimped to its support.

The filament is still intact.

The balloon envelope is 56 mm in diameter, and excluding the B4 base pins is 81 mm tall.

References: Observation.

Pin Connections

Absolute Maximum Operating Conditions^¶