e AmatGur • 

 Electrician 



^d Wii'dess Operator 



Easily Constructed Step-Down 

 Transformer 



THE greater part of the work of building 

 a small step-down transformer is in 

 the cutting and assembling of the iron. By 

 securing the reactance core of a dismantled 

 alternating current arc light there will be 

 had a well proportioned and efficient core 

 ready for taping and winding. These cores 



A laminated iron core of a discarded arc 

 lamp used for a step-down txansformer 



can be easily secured as, in a great many 

 places, the new high powered Mazda and 

 nitrogen lamps are replacing the old style 

 arcs. The core I used was of the dimensions 

 shown in the accompanying illustration. 



File the sides of air gap smooth and 

 parallel; clean the iron, tape and then 

 shellac it. When the shellac is dry wind 

 on No. i8-gage double cotton-covered 

 copper wire in even turns. For a maximum 

 secondary voltage of 12 volts wind 120 

 turns, starting i in. from the opening on 

 the inside circumference. Tape may be 

 taken off at any turn, figuring ten turns 

 for each volt. Wrap the secondary coil 

 with linen tape, and cover with shellac. 

 Over this wind iioo turns of No. 26-gage 

 double cotton-covered copper wire as 

 evenly as possible. Cover the completed 

 primary and core to the opening with 

 black friction tape and then coat it with 

 shellac. Cut a disk of J^in. fiber and bore 

 holes for binding posts as shown. Slip a 

 piece of J^-in. cotton tubing or lacing over 



each lead and connect it to the binding 

 posts. Fasten the fiber to the transformer 

 by t>ing it with cloth tape. 



The proper and efficient way to fill the 

 air gap would be to cut small pieces of 

 transformer iron and wedge them in place 

 in line with the other laminations. Another 

 way is to cut pieces of the metal i^ in. 

 long by I in. wide, and drive them in at 

 right angles to the core iron. This latter 

 method causes the wedge to heat up, 

 showing there is considerable loss through 

 eddy currents. For most experimenters 

 the transformer will operate efficiently 

 enough with gap left open. — O. J. Hurlbut. 



One Telephone Used 

 on Two Lines 



WHERE it is desired to use one tele 

 phone on two lines so that both 

 lines will be kept separate and yet sound 

 the rings from each line, the following 

 rnethod may be used. Connect an. exten- 

 sion bell and a double-pole double-throw 

 switch to the telephone and the lines, as 

 shown in diagram. 



If one of the lines is a grounded circuit, 

 the ground should be connected to one side 

 of the switch and not to the telephone or 



W BtLL SWITCH TELtPHOSE 



Connections of telephone wires and bells 

 for using one telephone on two lines 



bells; but if both are grounded circuits the 

 common wire should be connected to the 

 ground. 



In the diagram, if the switch is thrown 

 up, the telephone is connected to the line i 



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