What Radio Readers Want to Know 



Calculating Wavelengths; Circuits of 



Audion Amplifier ; Helix for 



Spark- Coil 



E. B., Pittsburs, Pa., inquires: 



Q. I. I have a loading coil for an inductively 

 coupled receiving luner consisting of 625 turns 

 of No. 22 enameled wire wound upon a tube 

 5J in. in diameter, also a secondary loading coil 

 wound with No. 27 enameled wire for a distance 

 of 7 in. on a similar size tube. Approximately 

 what is the wavelength of each? 



A. I. We cannot give the possible wave- 

 length adju.stment of a coil without knowing the 

 constants of the circuit in which it is to be 

 employed. It is easy to calculate the natural 

 wavelength, but this data would be of no value 

 for ordinary usage. The primary loader has 

 inductance of approximately 12,400,000 centi- 

 meters and the other coil about 15,875,000 

 centimeters (15,875 microhenries). You of 



l)ut with .001 microfarads in shunt the wave- 

 length of the circuit is about 7000 meters. 



Q. T,. I require two loading inductances for 

 this set to be adjustable to 14,500 meters in 

 steps of 500 meters at a time; but they cannot 

 occupy a space more than 8 in. by 5 in. by 3 in. 

 Can you supply the data for the windings? 



A. 3. We know of no method by which you 

 can obtain this value of wavelength with a coil 

 of these dimensions unless you wound it with 

 very fine wire which, of course, would make 

 them useless. Also keep before you the fact that 

 there are no stations in o[)eration that use the 

 wavelength of 14,500 meters. Why not con- 

 struct a set like that described by McKnight in 

 the April, 191C, PopirLAR Science Monthly? 



Q. 4. Can you furnish me with the circuits 

 of the single step Audion amplifier? 



A. 4. See the accompanying diagram. 



Q. 5. What is the voltage of the filament 

 battery? 



Diagram showing the circuits of the single step 

 Audion Amplifier 



PH0NE5 



"iRy 



course understand that the increase in wave- 

 length to be obtained with a given loading coil 

 depends upon the natural inductance and 

 capacity of the circuit in which it is to be con- 

 nected; consequently, if these values are un- 

 known, no general estimate can be given. You 

 will then see that there is no such thing as a 

 "2800 meter loading coil" even though manufac- 

 turers are prone to use the notation. 



Q. 2. My Navy type receiving tuner has a 

 primary winding consisting of a single layer of 

 No. 20 enameled wire wound upon a tube 

 4i in. in diameter for a distance of 5 in. The 

 second. iry tube is 3J in. in diameter, wound for a 

 distance of 5 in. with No. 30 enameled wire. 

 What is the maximum wavelength this tuner 

 will respond lo? 



A. 2. Lacking the dimensions of the aerial it 

 is difficult 1(1 .nlvise; but with one of the usual 

 am:ilcur dimensions, the primary circuit is 

 adjustable to waves of 45<m) meters. With a 

 capacity of .o<k)I microfarads in shunt, the 

 secondary < ire nil will r<s|K)n(l to 2400 melcrs 



A. 5- 



Q. 6. 



battery? 



A. 6. 



Q. 7. 

 A. 7. 

 Q. 8. 



4 volts. 



What is the voltage of the second 



25 to 45 volts. 



Is the Audion tube suitable for this ? 

 Yes. 



Can you give me the voltage of the 

 telephone battery in the RJ5 Audion? 



A. 8. 25 to 45 volts. 



Q. 9. What type of battery cell is used? 



A. q. A 20-ampere hour storage cell for the 

 filament and 10 tungsten flashlight cells for the 

 telephone battery. 



O. 10. Mow many turns of edgewise wound 

 copper ribbon 7J in. inside ciiameter, 8J in. 

 outside diameter, 1-16 in. in ihickne^is, are 

 required as a helix for a yin. spark coil? 



A. 10. The helix rc(|uiros 10 turns of the 

 copixT spaced 5 in. apart. A condenser of .tH)2 

 mirrofar.ids is sufTicient. A single plate of gl.iss 

 14 in. by 14 in. covered with ihin foil 12 in. by 

 12 in., the glass iK-ing J in. in thickness will give 

 the required value of c-ijiacity. 



(i:iu 



