Popular Science Monthly 



condenser across the telephone terminals 

 with an audion detector, however used. 



The leads to condenser 15 must be 

 amply protected against any possibility 

 of shortcircuiting the high-potential 

 battery. If a telephone-type condenser 

 is used, after the leads are soldered to the 

 lugs (which are close together) it is a good 

 plan thoroughly to cover the lugs, the 

 solder, and the wires which are exposed, 

 with sealing wax or paraffin. Condenser 

 II must be one that does not "contact" 

 inside, for a shortcircuit of the high- 

 potential battery is possible when all 

 inductances are tuned out. It is a good 

 idea to insert a 3^ ampere fuse in the high- 

 potential battery circuit. 



Condenser 1 1 is the one most handled 

 in tuning. It is used in conjunction with 

 inductances 13 and 14 to bring the wing 

 circuit into resonance with the secondary 

 circuit, and cause the bulb to oscillate. 

 In the wiring diagram, 16 shows a volt- 

 meter across the filament terminals; 

 though not positively necessary, it is 

 useful. If one gets accustomed to regu- 

 lating the lighting voltage with a volt- 

 meter, the likelihood of "crowding" the 

 filament is almost eliminated, and hence, 

 a longer life of the bulb may be expected. 

 The bulb may be shaded to prevent 

 strain on the eyes. In the diagram, 17 is a 

 pole-changing switch provided to reverse 

 the lighting battery ; it is a very desirable 

 adjunct. Any d.p.d.t. battery switch 

 will do. 



Condenser 7, usually used to tune the 

 secondary, is not necessary with this set. 

 Tight coupling is employed with long 

 waves. Any necessary variation of ca- 

 pacity for short waves may be effected by 

 slightly changing the coupling. The 

 fixed condenser usually found within 

 each audion detector, in series with the 

 grid, should be removed or bridged over; 

 the variable condenser 8 takes its place 

 in this set. 



Assume, now, that we have assembled 

 these component parts and wish to "pick 

 up" Tuckerton, Arlington, or Sayville — 

 stations working with long wavelengths 

 of from 6000 to 8000 meters: 



Couple the tuner closely; throw in all 

 of the aerial tuning inductance and those 

 of both primary and secondary of the 

 tuner; throw in all of the secondary 

 loading inductance; set condenser 8 at 



615 



about half capacity (according to the 

 scale); set condenser 11 at zero; throw 

 in all of inductance 13 and about half of 

 14, adjust the lighting and high-potential 



Arrangement of complete receiver 



batteries as usual, then slowly turn up 

 condenser 11. 



The lamp should begin to oscillate, and 

 this will make itself manifest by a 

 peculiar muffled "boiling" sound and a 

 change in the sound of static. A loud or 

 troublesome hissing sound indicates too 

 much high-potential or lighting voltage, 

 or both, and should be avoided; the bulb 

 is not in its most responsive condition 

 when this is present. A very slight blue 

 glow is usually observable in the bulb, 

 back of the wing, when it is doing its 

 best. If immediate results and signals 

 are not secured, raise and lower the high- 

 potential and lighting voltages in various 

 combinations and manipulate condenser 

 II until the bulb oscillates. Swinging 

 condenser 8 through its arc, and chang- 

 ing the polarity of the lighting current 

 may have important effects — it depends 

 upon the bulb. 



Not all audions oscillate with equal 

 facility, but I have never handled one 

 that would not oscillate with a little 

 patient persuasion. Holding a lighted 

 match to the bulb until the glass is ver%' 

 warm tends to break down its unwilling- 

 ness to oscillate. The sensitiveness of a 

 given bulb while oscillating seems to be 

 directly comparable to its sensitiveness 

 in ordinary use. Since not all audions, 

 nor even both filaments in any one 

 audion, are equally sensitive, this should 

 be kept in mind so that one will not 

 expect an insensitive bulb to give the 

 finest results, under any conditions. 



