Does anyone know what this is!..???
 

Hi

Found this in a mixed box, no markings, 4 pins, no idea !!:D

http://i1155.photobucket.com/albums/...2/IMAG0641.jpg

Its a ballast tube , a resistor in a tubes envelope .

a test dummy for production?

It is a ballast tube, which is not a pure resistor. It is a tungsten heater with similar characteristics to the heaters in the tubes it was designed to work with. Old radios often had their heaters wired in series and connected to a power source. This was often the line voltage, but could be 28 or 48 volts in aircraft or marine systems. A ballast tube was added to absorb the difference between the source voltage and the sum of all heater voltages. Obviously each application requires a tailor made ballast tube.

Thanks guys.....display tube I think they call them on Ebay :)

Could be iron-hydrogen resistor.
In that case it has an iron filament (not tungsten) and the gas inside is hydrogen.
Iron-hydrogen resistor - Wikipedia, the free encyclopedia
works like a constant current device - sort of - when connected in series
iron has a much lower melting point than tungsten, when it glows slightly red it is already close to melting; don't apply voltage unless you want to distroy the filament
they were not glowing during normal operation !