286 



Popular Science Monthly 



A Quenched Gap with Metal Spacers 



IX designing quenched spark-gaps a 

 number of inventors have attempted 

 to produce dischargers in which the 

 spacing of plates, or length of gap, would 

 not be determined by the pressure 

 applied to the gaskets separating the 

 elements of the gap. When thin press- 

 board or rubber composition gaskets are 

 used under heavy pressure, the gaps 

 sometimes become too fhort. This is 

 especially likely to happen when the 

 apparatus grows hot after long use. 

 A method of construction patented by 

 R. Pfund in late 1915, and shown in 

 specification 1,161,520, from which Fig. i 

 is reproduced, avoids some of these 

 troubles by using metallic spacing- 

 washers. The gap elements are made up, 

 as shown in this drawing, from base 

 plates 4 which have attached to them 

 the raised sparking-surfaces 18. Insula- 

 ting-rings 5 support metal rings 6, and, 

 after the half unit consisting of 4, 18, 5 

 and 6 is assembled the active gap surface 

 18 is turned off so as to be exactly in ths 



.'ra 



>5 



Fig. 1. Metallic spacing washers used in 

 the new quenched spark-gap 



plane of the ring 6. Thus, when the 

 metal spacing- washer 7 is inserted, the 

 two sparking surfaces are held apart by 

 it at exactly the right distance. Heat 

 will not affect the washer 7 to any great 

 degree, and its thickness can be made 

 more nearly uniform than when thin 

 insulating material is used. Of course, 

 the true spacing will be held only so long 

 as the insulating-rings 5 hold their 



shape; these, however, are far more 

 rugged than the usual gaskets. 



The complete assembly of the gap is 

 shown in Fig. 2. Units built up as in 

 Fig. I are supported upon the two lower 

 rods 10, and between them are inserted 



Fig. 2. The single units are built up in 

 this form to complete the gap 



larger cooling plates 8. The compression 

 screw 16 serves to make the gaps prac- 

 tically air-tight, in the usual way. This 

 construction makes demounting easy, 

 since, immediately upon loosening 16, 

 any of the elements may be removed for 

 inspection or cleaning, without disturb- 

 ing the cooling plates or the other gaps. 

 If, when rubbing down the surfaces, the 

 entire assembly 4, 18, 5 and 6 is slid 

 over a flat polishing cloth, the active 

 plane is maintained accurately in line 

 with the surface of disk 6. The constant 

 and accurate spacing maintains adjust- 

 ments which gi\e a clear spark tone. 



Switch Points for Radio Instruments 



VERY neat and serviceable switch 

 points may be made of round 

 brass rod of the diameter to suit one's 

 refjuirements. All that need be done is 

 to drill and tap the end of the rod and 

 then cut off the length giving the 

 desired height of switch points. A 

 machine-screw is to be used for fastening 

 it to the instrument panel. — Louis Lind. 



Make your switch points from pieces of 



brass rod by tapping the end and cutting 



it off at the proper length 



