ABSTRACTS OF TECHNICAL ARTICLES 141 



operations. Of particular interest are the use of special progressive punch 

 and die tools, coil winding, contact welding and conveyorized assembly and 

 adjustment. 



The use of heavy presses with large progressive punches and dies was 

 necessitated by the degree of accuracy required for this grade of equipment. 

 For example, the vertical unit base, weighing only f lb., is produced by a 

 75,000 lb. press, using a 3,500 lb. tool. Again, since 40,000,000 contact 

 springs are required annually, each of which must be attached to insulators, 

 automatic presses, conveyor belts and handling devices are required. Weld- 

 ing two contacts on each spring is accomplished by special welding presses 

 using rolls of contact metal tape, each contact being cut off just prior to 

 the welding process. A quality of less than one defective contact out of 

 20,000 is maintained. 



The coils are wound in special machines in "sticks" of 5 to 7 coils with 

 .0007 inch thick cellulose acetate between each layer. A wire of a gage size 

 halfway between ^37 and #38 B & S is used on most of the coils because 

 of critical capabiHty conditions — the annual amount of wire of this size 

 being 125,000 lbs. 



Assembly and adjustment of the switches proceeds on conveyor belts 

 from one end of a large room to the other — the procedure being set up in 

 such a way as to create a continuous flow of completed parts for wiring into 

 the large frames ready for installation in telephone exchanges. 



Regulated Rectifiers in Telephone Offices}- D. E. Trucksess. For many 

 years rectifiers of the garage type were used in converting alternating cur- 

 rent to direct current for charging batteries used for communication pur- 

 poses. These batteries furnish power for relay operation, for talking, and 

 filament and plate supplies for repeaters. The rectifiers were of the manual- 

 control type where the operator selected the charging current by means of 

 tap switches or rheostats. 



With the development of the thyratron type of tube, a rectifying means 

 was made available in which the grid of the rectifier tube could be used to 

 control its own output current by an electronic circuit. Rectifier circuits 

 were designed to maintain a constant output voltage. If a regulated recti- 

 fier is connected to a battery and the constant rectifier voltage is 2.15 volts 

 per cell, the load current will automatically come from the rectifier and not 

 from the battery. Also the battery will draw from the rectifier sufficient 

 additional current to maintain its charge. If the circuit voltage is held 

 within limits of less than plus or minus one per cent, the maintenance of 

 the battery is reduced and its life is extended. 



The thyratron tube differs from the vacuum tube in that the grid does 



^^ Elec'L Engg., Transactions Section, August 1942. 



