The 4104E is part of a family of repeater valves, 4104D, 4104E and 4104G. The 4104E has a filament designed to reduce sputter noise. The maximum anode dissipation is 5 Watts but the output power is given in the data-sheet as 300 mW maximum.
The 4101D type has an anode impedance of 5,000 Ω whereas the 4104 type has the lower ra of 2,000 Ω and is designed for higher power output.
In 1946 STC replaced the 4104D with the 3A/141AY. The 3A/144AY was a specially tested sub-set of 3A/144A production.
The construction uses the characteristic vertical glass rod support and the ladder grid. The filament is an inverted V with grids and anodes either side. Note the locating pin on the side of the plastic base cap.
The base cap has lettering pressed into the plastic. Looking at the filament suggests that there is oxide coating only on the middle section of each leg.
The balloon envelope is 59 mm in diameter, and excluding the base pins is 94 mm tall.