THE WORLD'S ADVANCE 



121 



prevent taking off the stain, var- 

 nish or shellac. Only No. oo 

 sandpaper should be used. 



While the varnish is drying, 

 work may be started on the in- 

 ductive tuners, requiring: 



Fiber about I sq. yd. 1/64 inch 

 thick. 



Wire i Yz. Ib. No. 30 s.s.c. and i 

 Ib. No. 22 s.c.c. 



COUPLER PRIMARY: Turn or 

 plane up a cylinder to the size 

 shown in Fig. 2. Cut the card- 

 board or 1/64 sheet fiber into 

 strips 2}4" wide, thus forming a 

 tube of the material about 3/32" 

 thick. For adhesive material use 

 shellac, or, better still, hot glue. 

 When the cylinder has been 

 formed, wind a piece of tape 



Wooden Spools Which Are Used for Holding the Secondary 

 Windings of the Coupler. 



around 



wind a 



it to hold the layers together, and after 

 allowing it to set for a minute remove 

 from the form. The cylinder should be 

 permitted to stand over night and the 

 superfluous glue then washed off, care 

 being exercised so as not to unloosen the 

 layers. When the cylinder is dry it is 

 trimmed to size on a lathe, or fastened 

 to a disc that can be rotated. 



The first primary is wound with thirty 

 turns of No. 22 s.c.c. wire, fifteen turns 



-et 



Primary f j Primary *2 



fio.3 



The Two Primary Coils, Showing the Method of 

 Winding. 



per side, spaced as indicated. The wire 

 is started through a hole bored in the 

 tube several turns of the wire being 

 passed through the holes to insure hold- 

 ing the winding being placed on the 

 cylinder as tightly as possible, fastening 

 the wire as in starting. Two or three 

 coats of thin, transparent shellac are ap- 

 plied when the winding is completed. 



For the second coupler primary five 

 small holes are bored, using a 1/16" drill, 

 about }4" apart and J^j" from edges, as 

 indicated in Fig. 3. One hundred and 

 twenty-five turns of No. 30 s.s.c. wire 

 are wound on, taking taps at 15, 30, 45, 

 60, 80, zoo, 125 turns. In taking these 

 taps, the wire is pushed through a hole 

 in the cylinder, the double wire being 

 then wound as shown, giving it several 

 turns similar to the method of starting, 

 leaving about a foot of doubled wire pro- 

 jecting. The winding is put on as tight- 

 ly as possible and then given several 

 coats of shellac. When dry, a strip of 

 single thickness empire cloth is wrapped 

 on. On top of this 30 turns of No. 22 

 s.c.c. wire are wound, starting and wrap- 

 ping as on the first tuner. Shellac is 

 applied when the winding is completed. 



COUPLER SECONDARIES: Turn up the 

 cores of ash or maple to the size indi- 

 cated in Fig. 4, taking particular care 

 that the radius of curvature of the sur- 

 face is the distance from the central point 

 on the axis to a point on surface. It is 



