• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

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

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Tubelab_com

Tubelab_com

Member
Joined 2005
tubelab.com
Its a ballast tube , a resistor in a tubes envelope .
Click to expand...

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.
 
Sorento

Sorento

Member
Joined 2008
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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