The DE5B is a dull emitter triode designed to be used as a resistance-capacitance coupled audio amplifier. The amplification factor of 30 and the high impedance all suggest that this valve was designed as a driver for the DE5A output valve.
The DE5B was the final valve in the family with DE5 and DE5A as well. This valve is half silvered showing that the valve was magnesium gettered and this is typical of all three.
The evacuation hole in the pinch is visible on the left and the fine wire grid as in the centre. The discolouration of the supports shows where the spot welds were made during assembly.
The envelope dome has the type designation etched into the glass. Also, inside the envelope, we can see the grid structure more clearly, together with the filament tension spring assembly. The grid is wound to a tighter pitch than the DE5A as one would expect to achieve the better gain.
The balloon envelope is 55 mm in diameter, and excluding the B4 base pins, is 92 mm tall.
References: 4051 & 1003 Type DE5B was first introduced in 1924.