Page:Popular Science Monthly Volume 89.djvu/300

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��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

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��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

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