While nitrogen is one of the gases used in lamps, Amperite ballasts typically use hydrogen or helium. Hydrogen isn't exactly inert, but it will prevent oxidation of tungsten and reduce any oxides. It also has a very high thermal conductivity.
Amperite Ballasts
John
Quote:
Originally Posted by jshorva65
Thanks, John! There's an excellent video on YouTube in which Bob Andersen (bandersentv) demonstrates the inrush-absorbing properties of the Ballast (using the Amperite glass replacement). We're using one of the Amperite units in a client's Motorola 7" set (TS-4H chassis). We just received the part from vacuumtubesinc. At $25 each plus $7 shipping, it's somewhat pricey unless you order multiple items (the $7 is a "minimum" shipping charge which covers shipping for the first 6 items on an order). Yes, they are pricey, but the cost is justified considering the difficulty of attempting to replicate the part with ordinary resistors and the fact that the Amperite unit provides both the voltage-dropping and inrush-limiting functions without the complex calculations required to incorporate thermistors or their equivalent into a substitute resistor array. My guess is that the Amperite ballast is probably filled with nitrogen (typical of standard incandescent light bulbs rated over 25 watts, incidentally). The use of nitrogen assists heat transfer to the glass (unlike a vacuum) while eliminating oxygen (which was the main cause of ballast failure in open-air units due to oxygen's corrosive effects on metals at high temperatures) from the resistance elements' environment. Nitrogen has been used for many years in standard light bulbs to better utilize the glass envelope for cooling, and to counteract atmospheric pressure (improve structural strength and prevent bulb implosion in case of breakage).
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