This valve is a mystery apart from the maker's name on the base cap. It is a triode and fully gettered but with an open circuit filament and no markings on the bulb it is not possible to say more.
Frelat valves were made by M Heussen & Co of Arnhem in the Netherlands and exported to the UK between 1926 and 1928.
There are some letters - pp4 on the glass but they do not match and of the Types in the data file.
The base is informative: Made in Holland and the Frelat logo. The pins are simple brass split pins.
Inside are two triode sections in parallel. Under the microscope the structure of one can be seen. The single strand filament is oxide coated, the helical grid is fixed to the support on one side only and the anode is shaped to offer a greater surface area than a plain cylinder. The suggestion is that this could be an output triode. Frelat made four output triodes.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 105 mm tall.
