RESISTANCE DEVICES 135 



proper insulation between the halves. The effective inductance 

 is about +0.05 microhenry. 



Ten-ohm Coils. Only the inductance need be considered. 

 Three 30-ohm coils are used in parallel. They are bifilar wound 

 on spools 2.5 cm. in diameter, a single layer of double silk-covered 

 manganin wire 0.24 mm. in diameter being employed. The 

 effective inductance is approximately 0.3 microhenry. 



One -hundred ohm Coils. The coils are bifilar wound in one 

 section, a single layer of double silk-covered manganin wire 0.24 

 mm. in diameter being used. The capacity effect preponderates, 

 resulting in an effective inductance of 1.6 microhenrys; the 

 phase angle at 2,000 cycles per second is about 35". 



One-thousand-ohm Coils. Five sections, each of two hundred 

 ohms, are used in series. Each section consists of a single layer of 

 doubhi silk covered manganin wire 0.10 

 mm. in diameter. The five sections are 

 bifilar wound on a spool 2.5 cm. in diam- 

 eter, a space of 2 or 3 mm. being left be- 

 tween the sections. The effective induc- 

 tance is about 16. microhenrys. 



Five -thousand -ohm Coils. Five thou- 

 sand-ohm coils may be built up of five of 

 the above 1,000-ohm coils in series or the 

 bifilar winding may be replaced by that FIG. 60. Special 

 illustrated in Fig. 60. 



The coil is wound on a porcelain cylin- 

 der which is slit along a diameter for about two-thirds of its 

 length. Double silk-covered manganin wire is used. The wire 

 goes once around the bobbin, then passes through the slit and 

 around the bobbin in tb opposite direction back through the 

 slit. This cycle is repeated until the whole coil is wound. The 

 capacity effect is very small as there is only a small P.D. between 

 adjacent wires. The effective inductance is about +30. micro- 

 henrys. The disadvantage is the difficulty of winding. 



Ten-thousand-ohm Coils. These are constructed by using 

 in scries two of the 5,000-ohm units just described. The effective 

 inductance is about +100. microhenrys. 



In the following table are shown comparative results given by 



