The Birmingham age-herald., 1922-06-25
By JACK BINNs How to Buils transformers

How to Buil0 transformers Q. l. When 221a volts are applied to the primary of an audio- frequency transformer what Is the voltage in the secondary? 2. what is the ratio between the primary and the secon- dary of these transformers? g. Does l it differ in the transformer between the detector and the first amplifying tube and those transformers which are placed between the simplifying tubes alone? 4 What Is the current in the plate circuit of radio-frequen- cy tubes. detector tubes and audio-
 frequency amplifying tubes? 5. How can I make an audio-frequeney
 transformer 6. How can I make a radio-freQuency transformer ?--W. H. G.
 A. 1, The voltage in the secon- dary of the transformer will depend upon the ratio that exists between the primary and the secondary. This question cannot be answered unless tho ratio is known. ?. That varies in different cases. The usual Is 3:1. 5. For audio frequency they are all the same. {. The plate current in the radio frequency, detector and audio lamplifiers will depend upon a great many factors, and as they are not Sldltu tue dH5W SI CAHHOI De klRGil. As a general approximation, how ever, 1t will be In the neighborhood of from three to four mili-amperes. 1 5. In connection with the construc- ton of audiofrequency transform CTS these should be wound on a ss i inch core. The core itself Is made Iup of lamiAated iron in the form of an oblong with a center section di- viding the oblong into two squares
 The primary will be laid upon the center section and will consist of 1,700 turns of No. A enamel-covered wire. The primary must be so
 wound that there Is a layer of very fine ffin-impregnated paper around each layer. The secondary will consist of 20, 900 turns of No. A
 enamel covered wire, with each layer insulated in the same manner as above. When the windings are con- pleted the primary should have direct current resistance of 1.075 ohms and the secondary should have a direct current resistance of 1,1Qg ohms. The ratio of this transfor-
 mer will be 3 to 1. In other words, the secondary will have a voltage of STA where 22la are applied on the plate circuit. 6. As I have stated repeatedly in this department, in my opinion radio-frequency amplffica- ton by means of the step-by-step system, or cascade coupling. is still lin an experimental stage so far as short wave reception Is concerned. No real satisfactory transformer has been evolved as yet, in my opinion. The trouble does not lie so much with the transformer alone as 1t does with the transformer and vacuum tube combined It must be under stood that the vacuum tube has the property of capacity between its ele- ments and this property has very definite, specific value, which ma terially affects tho circuit. despite the fact that the capacity Is meas
 ured in micro microfarads With vacuum tubes being turned out on lproduction basis it is absolutely inn possible to get two tubes that are ] exactly alike in their capacity, and ithis Is a very serious problem when lit Is considered that the value of the capacity Is so very low. The result is that in practice the radlo-fre- louency transformer that may De somewhat successful with certain
 particular tube is absolutely unreii-
 able when a different tube Is placed 1 in the circuit. due to the reasons given above. Under the cfrcum- stances, therefore, would not duNisc
 its use. except for experimental pur- noses. at this time. In view of the remarkable results that have been obtained in Major Armstrong's new system, which is the real. true form
 of radio frequency ampiification on
 short waves, I should rather you would wait until the constants for this system are released and then experiment with them. In any case the transformer must be wound l specially for the wave length you |desire to receive.
 Pocket Set for Policemen
 O. will you please describe for lme the pocket radio sets which the
 IChicago policemen are now using to
 keep in touch with their headquar- iters?-R. J. M.
 A. I do not know the details (