Q Amateur - 

 Electrician 



Tf\nd WIi'gIgss Operator 



A Perfected Slider for Tuning Coils 

 in Aerial Apparatus 



A CONTACT for tuning coils that actual- 

 ly slides and does not scrape is illus- 

 trated. Ordinary sliders make such un- 

 reliable contact and wear out the wire so 

 quickly that they have generally been 

 discarded for the more cumbersome 

 switches. This slider is useful for both 



Rubber suoeRn mtol roo 



SLIDER \ 



WIRE ACTW6 AS RAC^ 



The metal gear-teeth mesh in the wire 

 coils in contact like a rack and pinion 



sending and receiving coils, though, of 

 course, the dimensions will be different for 

 each case. 



The slider is formed like a gear wheel. 

 The coil-turns serve as a rack, so that the 

 net effect is an almost frictionless direct 

 contact, turn by turn with the coil. Where 

 an ordinary slider makes only line contact 

 by friction with the wire, this slider 

 contacts a larger portion of the conductor. 

 The wire is wound in screw-threads cut 

 in a lathe into a composition non-warping 

 tube, so that the turns can be accurately 

 spaced. The wheel is cut from copper or 

 brass to match the coil pitch, though the 

 less exacting builder may use an old alarm- 

 clock wheel or even a knurled binding- 

 post. A pitch of 20 with corresponding 

 wheel about y% in. in diameter has been 

 found best for receiving coils. For the 

 inner coil of a loose coupler the wheel is 

 arranged to contact through a slit in the 

 tube from the inside, so that the secondary 

 may be moved in or out of the primary'. 



Of course a plain wheel may be sub- 

 stituted, but all of the good qualities out- 



lined will not be retained. This simple 

 improvement constitutes an important 

 betterment of this class of variable coils. 

 This, of course, is equally suited to rheo- 

 stats and other helical coils. There is 

 substantially no wear on the wire and 

 consequently no short-circuiting of turns 

 by burrs carried over by the erosion of a 

 friction slider. — P. E. Edelman. 



Fastening Binding-Posts on the 

 * Ends of Heavy Wire 



TAKE an empty rifle or revolver shell, 

 about a 32-caliber, and through the 

 closed end punch a hole large enough to 

 receive the screw of a binding-post. File 

 the screw off short enough and then push 

 it through the open end of the shell, through 

 the hole in the closed end, and screw the 

 parts of the binding-post in place. Clean 

 the inside of the shell and fill with solder. 

 Insert the end of the wire and heat well over 

 a blow-torch flame. Use soldering flux. 



ADJUSTING MANOIZ 

 LOCK KUT 



How to Make a Ten-Ampere Key 

 for Wireless 



THE contacts of the ordinary telegraph- 

 key are not large enough to stand the 

 current of a fair-sized transformer. But 

 by adding the contacts as shown in the 

 illustration any 

 telegraph-key 

 can be made of 

 J^in. sheet brass 

 bent as shown. 

 The end of the 

 stand A is drilled 

 and tapped for a 

 5/32-in. brass ad- 

 justing rod. 5, which is provided with a lock- 

 nut and adjusting handle. At the end of the 

 screw a small piece of silver — a dime will do — 

 is soldered and another is soldered to the rear 

 end of the key lever, as shown, with a hard 

 solder. The upright A should l>e pro\nded 

 with a binding-post, as the old contacts 

 of the key are not used. — Edward Jasper, 



B OWE CONTACTS 



Ordinary telegraph-key 

 with silver contacts 



147 



