The 4104D 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.
This exhibit was made by the Australian company and has the prefix SY. The brown base may indicate a moisture resistant composition for use in tropical environments.
In 1946 STC replaced the 4104D with the 3A/141AY. The 3A/144AY was a specially tested sub-set of 3A/144A production. Both retained the UV base but construction followed current practice of the time rather than the original.
The locating pin for the bayonet holder. Internally the anode flat plates are connected together with U shaped straps. The construction is double sided with a central filament.
The grid is of ladder construction and the electrodes are spot welded to the supports that are themselves embedded in the glass rod support. In this exhibit the glass rod is intact and all the electrodes are in their correct positions relative to one another.
Here the oxide coated filament can be seen. The oxide itself is cracked on both filament loops.
A closer view of the glass rod support and the detailed hand construction required to make this valve.
The UV base pins. There are no marks on the pins and it is possible that this valve has never been used.
Seen from the top the relative spacing of the electrodes can be seen. The filament is not held centrally and probably the performance of different specimens will have a wide spread of characteristics.
The balloon envelope is 58 mm in diameter, and excluding the UV base pins is 95 mm tall.