382 



THE WORLD'S ADVANCE 



through the hard rubber bushing in the 

 right-hand end of the cabinet to the con- 

 trolling handle. 



Fig. 5 is a side elevation of the cabinet 

 showing the side removed. Here may 

 be seen the three tiers of fixed couplers, 

 the receiving transformer and also the 

 method of mounting the adjustable con- 

 densers at the back of the front panel. 

 The upper one of the fixed tuners is 

 shown in section and discloses the sec- 

 ondary coil, the method of mounting the 

 same within the primary and the means 

 for adjusting the coupling. It may be 

 stated here that it is intended to have the 

 coupling in any of the fixed couplers 

 made as loose as is consistent with clear 

 reading, but in some cases, as in especially 

 long distance work, coupling may have to 

 be quite close. Consequently, the coupling 

 could not be made invariable as by wind- 

 ing the primary and secondary windings 

 side by side on the same form, which 

 would be a simpler construction. It is 

 intended that any change in inductance 

 of the associated receiving circuits oc- 

 casioned by the adjustment of coupling of 

 these fixed couplers shall be compensated 

 for by the adjustable condensers. The 

 coupling, however, is intended to be sel- 

 dom if ever changed when once stand- 

 ardized. 



Before proceeding to a detailed discus- 

 sion of the several parts comprising the 

 instrument, it will be well to show how 

 the fixed tuners are to be standardized. 

 To this end it should be noted that the 

 cabinet is to be completed in every way 

 and ready for the reception of signals 

 with the receiving transformer before the 

 fixed tuners are wound. The apparatus 

 is then connected up to the aerial and 

 detector and a station accurately tuned 

 in. In doing this both adjustable con- 

 densers are set with their rotating plates 

 half in their stationary plates. When 

 perfect resonance has been obtained, the 

 exact number of turns in use on the pri- 

 mary and secondary are noted. With 

 this data one of the fixed tuners is wound 

 with the same number of turns, as noted, 

 and the tuner marked with the call let- 

 ters of the station corresponding and 

 then laid aside. A second station is then 

 similarly measured up and a second fixed 



coupler wound to agree with it. In this 

 way the twelve tuners, or as many as may 

 be needed, are wound and provided for 

 as many stations. 



The next step is, of course, to mount 

 the same within the cabinet and make 

 the proper connections. Finally, when 

 each station represented among the fixed 

 tuners is picked up on the receiving trans- 

 former it is switched in to the fixed tuner 

 provided for it and the coupling made as 

 weak as possible, the adjustable conden- 

 ser's best position being also noted and 

 recorded along with the corresponding 

 station's call letter, etc. When the twelve 

 tuners are mounted and connected the 

 arrangement is similar to a telephone 

 switchboard at a central exchange, where 

 the operator can plug in any station de 

 sired without a volume of tiresome ad- 

 justments. 



Returning now to consideration of the 

 drawings, Fig. 6 is an assembly of the 

 cabinet proper containing the strips for 

 supporting the fixed tuners. This is best 

 made of mahogany, but whitewood 

 stained in imitation, or oak, may be used. 



Detail No. i is the bottom of the cabi- 

 net, with strips for connecting the tuner 

 supporting strips to the base and for re- 

 ceiving the front switch panel. 



Detail No. 2 is the top of the cabinet, 

 with similar strips. 



Detail No. 4 is for the left and the 

 right hand sides of the cabinet. It should 

 be noted that not all the holes shown 

 should be drilled in either piece, but that 

 they should be drilled exactly as noted 

 thereon. 



Detail No. 5 is the back of the cabinet 

 and is drilled for mounting fixed tuners 

 and accommodating the coupling con- 

 trolling rods for the same. 



Detail No. 6 is the front switch panel, 

 and is best made of hard rubber. The 

 popular dull finish on hard rubber can 

 be obtained, if desired, by taking off the 

 polish with fine pumice powder and 

 water. Hard fibre or even wood stained 

 black may be used in place of rubber. 



Detail No. 7 shows the coil forms for 

 the fixed tuners, and is self-explanatory. 



Detail No. 8 is the primary coil form 

 of the receiving transformer. 

 Detail No. 9 is its secondary coil form. 



