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This beautiful exhibit is a bi-grid bright emitter valve, probably originating in Holland. The dual grids have similar pitch and so this was probably made for reflex use rather than as a space charge grid valve. In reflex operation the signal is amplified twice by the one valve, once at RF and again at audio.

The envelope has no markings and so we can not precisely identify it.

The inner grid was normally connected to the side connection that is not insulated from the metal skirt.

In close-up the electrodes are revealed. Each grid is supported at the bottom by being attached to a horizontal support rod. The anode is an open cylinder with at the centre of the co-axial arrangement a single tungsten filament strand.

The balloon envelope is 47 mm in diameter and, excluding the B4 base pins, is 80 mm tall.

Reference: Observation.