q Amateur • 

 Electrician 



^nd Wireless Operator 



A coil of wire placed 

 between record disks 



A Simple and Attractive 

 Loading Coil 



ORDINARY loading coils are often 

 made in very compact form, as when 

 wound between two hard rubber disks. 

 Though very neat in appearance, such coils 

 are hard to make without the aid of 

 suitable ma- 

 chinery for 

 turning out the 

 rubber disk 

 ends, which 

 are expensive if 

 bought ready 

 made. If the 

 method of con- 

 struction de- 

 scribed in this 

 article is used, 



however, such coils can be easily made in a 

 few minutes at a very low cost, and not only 

 will they give the best of satisfaction, but 

 they will present a very smart appearance. 



The principal feature of this coil is 

 embodied in the ends, which are small ten 

 cent disk phonograph records. These can 

 be bought for about five cents apiece 

 second-hand at a record exchange shop, or 

 in many cases at the 5 and 10 cent stores, 

 wherever old records that do not sell well 

 are reduced in price. 



These composition disks are about $ l A i n - 

 in diameter, and can be separated any 

 desired distance by cardboard washers. 

 The remaining space around the circum- 

 ference of the cardboard and between the 

 walls formed by the records is wound with 

 fine wire, say about No. 28. The records 

 can be turned so that the grooved sides face 

 each other, thus leaving the smooth faces 

 turned out and displaying the patent dates 

 and numbers which are embossed on the 

 bottom of the records. 



The composition and cardboard disks are 

 held together by binding posts passing 



through them near the center, or by 

 several small copper rivets, arranged in a 

 circle. These rivets may be used as con- 

 tacts for a rotary switch, with which the 

 inductance of the coil can be varied. After 

 the holes for the binding posts and rivets 

 have been made, and before the wire is 

 wound on, all the disks to be used should be 

 shellacked together in the proper positions, 

 and dried under a flat weight of say 5 lbs. 



The coil illustrated is a single step affair 

 with only two binding posts. By making 

 two separate windings, and fitting the coil 

 with four binding posts, considerable ad- 

 vantage is obtained over the single step 

 type. With the latter scheme the instru- 

 ment can be used as a straight tuning coil 

 with two variations of inductance, or the 

 separate windings can be so coupled as to 

 form an inductive tuner. It can be used to 

 increase the wavelength range of primary and 

 secondary of any loose coupled tuning coil. 



Instruments made in this manner must 

 be handled with reasonable care, both in the 

 making and use, as the composition ends, 

 while almost as-strong as hard rubber of the 

 same thickness would be, are too thin to be 

 banged about indiscriminately. However, 

 in case of breakage the cost of renewal is 

 slight.— R. V. Clark. 



Using a Bicycle Pump for a 

 Water Rheostat 



A WATER rheostat can be quickly 

 made from an old bicycle hand-pump. 

 Remove the metal cap through which the 

 rod passes, and substitute a plug of wood or 

 cork. 



Through the center of this plug a hole 

 should be bored, its diameter being 

 identical with that of the rod. Next 

 remove the plunger disk and thoroughly 

 clean the rod so it will be free from grease or 

 rust. Wire leads should also be soldered to 

 both casing and rod for electrical coh- 



601 



