N-1 CARRIER TELEPHONE SYSTEM 419 



Important as these new system and circuit techniques are, they could not 

 in themselves accomplish the objectives of small manufacturing cost, mini- 

 mum engineering by the customer, ease of installation, and substantial 

 dimunition of maintenance effort. Contributing in large measure to the 

 overall success of the Type N System are new and interdependent features 

 in the components and equipment, which in combination represent a com- 

 plete transformation from the past. Miniaturized components and improved 

 assembly techniques yield large reductions in size and weight. Unitized 

 construction with packaged sub-assemblies not only simplifies installation, 

 but greatly facilitates the finding and correction of trouble, permitting 

 shipment of defective units to a central point for overhauling and thereby 

 making it possible to maintain the working equipment with plant personnel 

 not highly trained in carrier techniques. A further contribution to ease of 

 maintenance has been made in various instances by extension of the life 

 of components in order to avoid the necessity for frequent replacement. 

 These and other features of the Type N equipment are described in this 

 paper, which discusses first the components and their characteristics, and 

 then the design of the equipment assembly. 



Resistors, Capacitors, and Inductors 



The circuit arrangements of the N-1 System have been designed with 

 adequate margins to permit generous use of the low cost, small capacitors, 

 resistors and potentiometers in commercial manufacture. Deposited carbon 

 resistors find application where high circuit precision is necessary, while 

 vitreous enamel coated resistors are used where higher power dissipation is 

 required. 



Capacitances of several microfarads or more must be compressed into a 

 small volume for miniaturized equipment. Aluminum electrolytic capacitors, 

 which have been used for this purpose, have limited life due to the suscepti- 

 bility of aluminum to corrosion by common reagents and contaminants. 

 In the Type N System, high capacity, long life tantalum electrolytic capa- 

 citors of both polar and non-polar types find their first Bell System ap- 

 plication^. These tantalum capacitors are considerably smaller than the 

 aluminum type. Two types of tantalum capacitors are used. In the sintered 

 type the anode is made by pressing powdered tantalum into a compact shape 

 and then sintering in a vacuum furnace to weld the powder particles. This 

 creates a porous mass in which a relatively large surface area is exposed 

 for oxide fihn formation, and hence a large capacitance per unit volume of 

 material is obtained. In the foil type, two foil electrodes are wound in the 

 conventional manner into a cyUndrical unit with a paper separator. Size 



2 "Tantalum Electrolytic Capacitors," M. Whitehead, Bell Laboratories Record, October 

 1950. 



