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Dagwood 8th January 2013 07:08 AM

Does anyone know what this is!..???

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

Dagwood 8th January 2013 07:10 AM

battradio 8th January 2013 07:14 AM

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

ruben alstad 8th January 2013 08:03 AM

a test dummy for production?

Tubelab_com 8th January 2013 01:34 PM


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

Dagwood 8th January 2013 04:18 PM

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

payloadde 8th January 2013 08:03 PM

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 !

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