The 5840W is the special quality version of the EF732 pentode. It appears to be an updated version of the EF72.
The 5840 was designed for wide band HF amplification under adverse conditions where good reliability is required. These applications include military equipment and industrial applications. As it will maintain its emission when used with long periods operating at cut-off, application in computer circuits are a possible use.
Another application area is as a microphone pre-amplifier built into condenser microphones.
The 5840 designation is also etched into the glass. The three wire grids indicate a true pentode.
The heat-sink that this exhibit was fitted in.
Each tube is line with a corrugated sheet.
The thin glass tube envelope is 10 mm in diameter and, excluding the B8D base wires, is 32 mm tall.
References: Data-sheet & 3002. Type 5840W was first introduced in 1957.