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funny 21st March 2012 01:26 PM

valves tungsten filament
I learned from a site Psvane & Shuguang tubes | vacuum tube ,electron tube,
Shuguang Treasure valves(black valves) used Japanese Toshiba Thoriated tungsten filament, this material‘s electron emission stability, more longer life than normal tungsten filament, is there any scientific basis?

HollowState 21st March 2012 05:50 PM

From: Care and Feeding of Power Grid Tubes
A thoriated tungsten filament is one form of an atomic-film emitter. Thorium is added to the tungsten in the process of making tungsten wire. Typically about 1.5% of thorium in the form of thoria (thorium oxide, ThO2) is added. By proper processingf during vacuum pumping of the tube envelope, the metallic thorium is brought to the surface of the filament wire, and emission increases approximately 1000 times. The thoriated tungsten filament is also carburized. The small amount of tungsten carbide formed in the carburizing process reduces the evaporation rate of the thorium and thus increases the life of the filament. At a typical operating temperature of approximately 1900º K, a thoriated tungsten filament will produce a specific peak emission of about 500mA/cm².

For a thoriated tungsten cathode, peak and average emission are essentially the same. A thoriated tungsten filament is more tolerant of ion bombardment than an oxide cathode, and therefore, higher voltages can be applied to the tube.

funny 22nd March 2012 08:25 AM

Too professional, thank you very much.
What are the advantages of platinum grid?

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