This article describes the construction of United Wireless spark transmitters and associated equipment.
Wireless, May, 1909, page 3:

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    The manufacture of wireless telegraph instruments, in America, is embraced in three factories owned and controlled by the United Wireless Telegraph Company, two of which are located in Jersey City, N. J., and one at Seattle, Washington. In these factories everything which enters into the transmission and receiving of wireless telegraph messages, except motor generators, is produced.
    Naturally a manufacturing establishment, of the magnitude of either one of these factories, becomes sub-divided into a number of departments in which certain classes of work are done. A detailed description of each of these departments would take much space and as the photo reproductions (printed herewith) are much more illuminating to a mind which is untrained in technical expressions, only short descriptions of the principal operations embraced in the manufacture will be given here.
    Beginning at the Office, one sees draughtsmen, engineers and office help, who lay out plans for the manufacture of apparatus, who test the apparatus after completion and retain records of all the material which comes in and every part which goes out of the factory.
    Next in order is the Receiving Department, presided over by a man who has had years of experience in a similar position. This department receives all incoming materials, weighs and measures them, checks up the bills and sends them into the office for record. From this department the raw materials are distributed to the various departments for working up or to the stock room for storage, from which it is withdrawn on order as needed.
    The actual manufacturing is embraced in several departments, each doing certain work, which goes towards making up the completed apparatus.
    In the Machine Shop all metals are worked up into their proper forms and all the metal parts, from the smallest binding post and connections to the heaviest castings, are turned out by the machinists employed therein.
    The Woodworking Department embraces the making of boxes, cases and all wood parts which enter into the construction of and protection of the completed apparatus.
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    The Tansformer Department to the ordinary mind appears most interesting, inasmuch as the process of manufacturing transformers may be followed therein and easily understood. On the shelves of this department there are stored hundreds of spools of small wire, the copper in which is scarcely larger than the ordinary sewing thread. There are also larger spools containing larger wire for the manufature of large size transformers. In making a 1 k. w. transformer the fine thread-like wire is first drawn rapidly through a bath of hot paraffine on its way to the winding form, which is a spool placed between two cylinder discs of steel set on a rapidly rotating lathe machine. This winding results in the formation of a thin disc of compactly wound wire, the disc being about 10 inches in diameter and 1/8-inch thick, and is known as a "pancake." Each of these "pancakes" contains 1,000 turns of wire. These pancakes have their electrical resistances carefully measured and then are stacked with a thickness of insulation-impregnated cardboard between them. The ends of the wires, which project from each pancake, are then soldered together and the resistance of the entire stack is then measured, and if it is found to be correct within 2 per cent. is "passed" and turned over to the "mould man," who in turn puts it in an iron pan which he fills with hot insulating compound. It is then taken in charge by a man who operates the "vacuum pan" and pump, who places the iron pan with its hot wax and stack of "pancakes" in the vacuum pan, the lid of which is closed and the pump started until every particle of air is removed from the stack, thereby insuring that the insulating compound is everywhere in perfect contact with the wire. When all the air is removed the "pumped-out" stack is removed and allowed to thoroughly cool, after which its electrical resistance is again measured. These stacks are now selected, according to their electrical resistance, and each is placed in a close-fitting wooden box, the ends of the wires being brought out through two insulated openings and then additional insulation is poured in between the stack and the sides of the box after which it has its cover nailed on. These boxes are then placed in large case and the "secondary winding" is completed.
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    A bundle of fine, soft iron wire is then carefully wrapped with insulating tape and shellacked; over this are wound many turns of large copper wire, which is also carefully insulated with shellac after which it is allowed to dry or harden for several days before it is taken from the drying racks and put in the center of the three "secondary" boxes already described.
    These transformers when completed have the wonderful property of "stepping up" an alternating current from 110 volts to about 50,000 volts pressure. In each transformer about 75,000 feet of fine copper wire is used and as hundreds of transformers are completed each year, the amount of fine copper wire used in their manufacture will run up into the thousands of miles. The larger transformers are made in exactly the same way, differing only in the amount of copper used and its size. The finished transformers are subjected to a most thorough working test at a wireless station, located at the factory, to see if any weak points might develop in actual operation. If it is found to be perfect it is placed in the stock room or shipping room, for delivery.
    The transformers manufactured by the United Company are standardized in capacities and arrange from ¼ to 20 k. w. The ordinary marine equipment is usually supplied with 1 k. w. or 2 k. w. transformers.
    A department, which, to many visitors is as interesting as the Transformer Department, is that in which the "condensers" are manufactured. In this department several styles of condensers are made, for different uses.
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    One style of condenser consists of plating glass jars or tubes both inside and out with metallic copper. The jars being an improvement over the old style of "Leyden" jars which were coated with tin-foil and shellac, instead of copper. The method of coating copper directly on the glass consists of an electric dynamo and long wooden tanks filled with bright blue solution. In this solution the jars are suspended on hangers which revolve slowly, turning the jars in the tanks. The inside of the jars are filled with the plating mixture and a strong current of electricity is turned out, the action of which deposits the metallic copper, contained in the solution, onto the glass. From the plating tanks, the jars go to workers who trim off the upper edges of the copper, both inside and out. From these men the jars go to the wrapping department, where girls wrap them in tissue paper and place them in boxes for shipping or storing until needed.
    Another style of condenser is manufactured, in which the glass jars are placed in tanks and, after being connected up, both the tank and jars are filled with water. This style of condenser is termed a "Water Condenser."
    Another style of condenser is made by placing tin-foil on sheets of glass and laying one glass upon the other, the tin-foil being connected at the terminals.
    Sometimes in larger installations these sheet glass condensers are put in tanks and lubricating oil poured in on and around them. In this case the condenser is termed an "Oil Condenser."
    The Finishing and Testing Room, where the receivers, tuners, transmitters, switches, etc., are assembled and completed, shows great activity. Only the best of mechanics and instrument makers are employed in this department and the accuracy, quality and finish of the apparatus, which comes out of this department, is not excelled by any manufacturing establishment in the world. After an instrument has been completed and tested in this department, it is sent to the office where an electrical engineer carefully tests it again. If, as is generally the case, it proves to be satisfactory, it is delivered to the wrapping department from which it goes either to the store room or to the shipping department for immediate delivery.
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    A large proportion of the floor area of all the factories is taken up with the manufacture of special "wireless" work which is constantly being made under contract for the various Governments and Governmental Departments.
    The Repair Department, where "used" instruments which are shipped to the factory to be put in first-class order or overhauled, also presents a scene of great activity.
    The three factories controlled by the United Wireless Telegraph Company produce approximately a million dollars worth of "wireless" apparatus per year. Some idea of' the volume of this business may be obtained from the fact that six to eight men are constantly employed in packing and shipping "wireless" equipments, and scarcely a week passes without some or all of this force working over time.
    The photos printed herewith give only a partial idea of the extent and activity of the manufacturing departments of the United Company, for in taking interior views, in order to get distinct photos, they are best taken when the machinery is shut down and the men are out of the shop.
    The extent to which "wireless" has grown within the past twelve months is shown by the fact that to-day there is employed in America in the manufacture and operation of the "wireless telegraph." in the Commercial and Governmental Service, office employees, etc., between two and three thousand men, which number is growing every day as new land stations and boats are equipped and orders, from various parts of the world, for American "wireless" apparatus are received.
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