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This exhibit is an experimental prototype De Forest triode. The five connections are separately taken through the glass envelope. Sadly the glass is opaque and the electrodes are not visible.

It is possible that this valve was made with a soft vacuum as De Forest believed that some residual gas made a more sensitive device. The superiority of the hard vacuum triode emerged during WW1.

See also Audion, CF185 & DV-5.

The balloon envelope is 32 mm in diameter and, excluding the base pins, is 230 mm tall. The lower sphere is 42 mm in diameter. The frame is mahogany.

Reference: Observation & ¹⁰⁴⁷.