460 



Popular Science Monthly 



An Improved Crystal Detector 

 Stand 



AFTER many years of scientific ex- 

 perimentation with various kinds 

 of detector stands and contacts, the crys- 

 tal detector stand described below was 

 found satisfactory. 



The detector is of the ferro type, 

 mounted on a small box containing an 

 arrangement for moving the crystal. 

 The chief merit of the instrument lies in 

 the use of a direct differential screw 

 which insures perfect alinement. 



This differential screw consists of a 



Elevation and plan of a simple crystal 

 detector stand 



combination of an 8-32 screw and a 2-56 

 screw. It is made by drilling in the 

 end of the 8-32 screw a hole to be tapped 

 out with a 2-56 thread. A little patience 

 is required, for if the builder does not 

 center the hole perfectly the first time, he 

 must try again. This is where the suc- 

 cess of the instrument lies. A 2-56 screw 

 is to be screwed tightly into this hole. 



A hole should then be drilled in the 

 piece A, directly below the one in the 

 piece B, and tapped out for a 2-56 thread. 

 When the differential screw is screwed 

 in place and turned one complete revolu- 

 tion, it will lower 1-32", but at the same 

 time the piece A will be raised 1-56" by 

 the other screw, or in other words, the 

 piece A will be lowered 3/224". 



The rest of the standard is easily 

 made, as may be seen from the diagram, 

 the pieces A and B being of i/i6" brass, 

 %'' wide and of a suitable length. The 

 pieces C are of thin phosphor bronze or 

 brass %" wide and of suitable length, 

 and the pillars D of round or hexagonal 

 brass of any size to please the maker. 

 The parts are held together with 8-32 

 machine screws. 



A box of 14" oak about 51/2" by 3" 



by IV4" should then be made, the detect- 

 or being mounted centrally on the cover. 

 Two binding posts are put on the front 

 as well as the knob for the adjusting 

 arrangement. As will be observed the 

 adjusting arrangement includes a screw 

 with adjusting knob, the screw running 

 through the box, and the far end having 

 the thread filed off and resting in a small 

 hole bored in the back of the box. Jam 

 nuts are used in back of the front piece 

 to prevent the screw from coming out. 

 A small guide rod guides the piece 

 H, which is moved by turning the screw. 

 The rest of the arrangement can be seen 

 from tlie diagram. The disk cup should 

 be mounted eccentrically on the shaft N 

 so as to obtain a greater range and con- 

 tact for the mineral. The hole in the 

 top of the box should be small enough 

 so that the mineral will be held firmly. 

 The standard and mineral adjusting de- 

 vice are connected respectively to the 

 two binding posts. 



For a contact wire, a piece of very 

 stiff German silver or other resistance 

 wire (not iron) should be used, and 

 heavy or light contact can be made with 

 the point. No. 30 B. & S. is all right. 



Loose-Coupler Switch Arrangement 



A MAT FURS often wonder how they 

 can reduce the number of taps on 

 their loose-coupler and still tune accu- 

 rately. The following scheme has been 

 used successfully and it is found that it 

 not only saves money but the instrument 

 works more easily. Instead of tapping 

 every wire in the first ten and then every 

 tenth wire, a tap is taken from every 

 second wire in the first Hventy and after 

 that every tzventieth wire. Thus half of 

 the taps are done away with on the sec- 

 ond switch. This, of course, only tunes 

 in steps of two. To remedy this a separ- 

 ate single turn is added at one end of 

 the primary and arranged with an extra 

 two-point switch, so that this turn can be 

 used whenever needed. With this ar- 

 rangement, any possible number of turns 

 may be used and the trouble and ex- 

 pense of making several extra taps are 

 saved. Another advantage is that rough 

 tuning can be accomplished much more 

 quickly and, after a station is located, 

 the more accurate tuning can be done. 



