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14
RADIO AGE for October, 1926
receivers using up to the capacity of the rectifying devices, generally either the Raytheon or the Rectron.
While the regular line of Bradleyohms were doing well on work for which they were designed, it became necessary to design a new resistor for greater current carrying capacity. In order to do this the resistor housing was made larger, the graphite discs doubled in number although reduced in thickness, and greater safeguards added in the way of insulating factors, such as from the frame to the active elements. On account of an eliminator being a power device it was necessary that better insulation be provided and that new standards of inspection be set up. This was done after a little research work on the problem, and today we have in radio the Bradleyohm type E which was made especially for eliminator work.
An inspection of the AllenBradley factory at Milwaukee recently made by the writer de
veloped a number of interesting features in connection with the manufacture of graphite resistances. This substance was found years ago to be an excellent resistance material and the AllenBradley interests adopted it as their standard for resistance material. It was and is used in the makeup of their industrial controller equipment, such as motor starters, overload relays and other current controlling devices known more intimately in the electrical field.
Carbon to Graphite
DISCS making up these resistance units are originally in carbon form. They are heated in an electrical furnace to 5500 degrees, Fahrenheit, and after 72 hours ensue as graphite. The electrical furnace which the writer observed had a capacity of 60,000 of their largest controller discs to 2,500,000 of the size used in the Bradleystats.
A battery of disc making machines take the powdered carbon, form it into discs, then stack it
The Magazine of the Hour
and tie automatically in packages ready for the electric furnace. The capacity of each machine is 45,000 discs per 8 hour day and there are a large number of them necessary to make up the rated output of the factory.
Rigid inspection tests are applied to all apparatus to insure its meeting requirements both as to accuracy of resistance and insulation factor. This results in diminishing to almost a negligible quantity the return of material due to poor assembly.
Some views of the various departments are shown in the pictures illustrating this story, the one of the chemical laboratory being interesting because not many readers know that chemistry is playing a greater part in radio than it was ever thought capable of doing. In fact the impression received after visiting the Allen-Bradley organization is that highly trained, specialized men are more in demand than ever and this company makes good use of all the data that science and research affords.
In this view are shown drill and punch presses in operation, the punch press department in the background