The Radio Valve

Radio Record, Volume II, Issue 7, 31 August 1928, Page 31

The Radio Valve

N article recently dppeared in the "Reeord" dealing with the function of the receiving valve. It now remains to elaborate, a little, its construction, and for this acknowledgment is due to Ernest Kauer, chief engineer, C.E. Manufacturing Co., New York. A radio valve, in short, is a device consisting of a nuinber of electrodes (terminals of an electric source), contained within an enclosure almost devoid of air. A modern valve calls for the closest selection of all materials entering into its construction, as well as the greatest care in handling all of these materials during the process of manufacture. | Variety of Glass. is used, not because it allows * light to pass through, but because it furnishes a substance which can be readily moulded into desired shapes, a substance which at the same time possesses high insulating qualities, com- > -ratively great strength, and the valuable property of opposing the passage of gasses of all kinds. Different kinds of glass are used ag their particular properties become necessary. Brass, because of its strength, freedom from corrosion, conductivity, and its ready ability to solder, is utilised for contacts and pins.

The Filament. | [N the manufacture of the filament two elements, Tungsten and Thorium, are employed. The former, hardly any more brittle than steel, is used because of its ability to sustain extremely high temperatures without fusing or melting. In this respect it is more durable than platinum. Thorium, an element which has come into prominence during the last decade, is one of the radio active group of which radium is the most valued member. When heated, thorium emits a copious flow of electrons, and on which the whole function of the valve hinges. A tungsten filament is impregnated with as much thorium as it is possible to cause it to dissolve. The valve of the filament wire used depends to a great extent on the amount of thorium it carries, as its exhaustion marks the ‘termination of the useful life of the valve. This accounts for a valve going "dead" rather than burning out. Overloading a valve, incorrect plate voltage or grid bias causes this supply to be rapidly depleted. @OME of the newer types of- valves namely A.C. and .25 amp. valves. use oxide coated filaments. These oxides may be strontium, barium and others, while the base metal may be nickel. This type operates at lower temperatures and has a higher "saturation point’ (the point at which a filament will burn out). Molydenum is a metal which, despite a high degree of temperature, retains its mechanical strength and is used in the construction ef grids and hooks ta support the filaments. Bakelite is usually used for the _ bases. | Magnesium, which. has previously existed in thé form of a small piece of metal welded on to the plate of the valve is suddenly released as a vapour or gas and performs the mission of creating a perfect operating vacuum. The magnesium vapour instantly condenses er deposits itself on the inside wall of the glass bulb and imparts to it the familiar silver-like look.