WIRELESS NEWS.

Press, Volume LXIII, Issue 18918, 5 February 1927, Page 10

WIRELESS NEWS.

| A.F. TRANSFORMERS. HOW THEY ARE .MADE. 'srncuLi.r kkittes roa the r.irss ) (Dy "Elcctra.'') When you examine an audio frequence - transformer it looks comparativelv simple. There doesn't seem' to he much to it except a metal case, a laminated core, a coil of fine wire, and lour miniature terminals for connexions. Once you connect it up in a radio set, a transformer seems even simpler than before. Use the proper U voltage and the correct C bias, and the transformer docs the rest. There urc no. intricate adjustments, nothing to get out of order or bother with. But, you ask, is there really anything so difficult or complex about building ;i high quality transformer? The answer is: Have you ever wound 2} miles of 4T wire on a small bobbin about an inch in diameter: UndoubtedIv you haven't, or if you have by any remote chance, you made up your mind that an audio frequency transformer is :i lot more complicated and harder to build than it looks from the outside. However, the winding of the wire on tlie forms is far from the whole story of successful construction. The heart of any transformer is the windings and the core. Upon these every manufacturer concentrates his attention. Before the winding is started the wire must he tested for pin-holes in the enamel insulation. This is done in automatic machines, feeding the wire through a mercury bath with a potential of eight volts between mercury and wire. Each fault in the insulation of the wire is registered on a graphic recording device, which shows tho total number of faults per foot of wire. If below the accepted standard, it is rejected. After testing the reels. go to the winrliiiE machines. Here the wire is fed to tho foils which are wound on special forms. Two and a half miles of wire is wound on the forms used for the coils of one transformer. Of course, wiwlin • the coils by hand would ho impossible. So line is the wire that it lias to be fed under very slight tension by specially designed machinery, with allowance made for the difference in sticed 'if windinrr reels as the hulk of wire on the form increases. Revolution counters insure the correct number of turns. When the coils are complete tliev pass on to the assembly rooms. Kadi coil is placed over an iron core in a special niece of testing apparatus, where a milliampuieler shows instantly anv short turns. Coils showing any defo. :.s are immediately rejected. The nest stage is the building of the cores into the bobbins of wire. After this llie tcrinin.il block is attached to the core, and connected to the windings. In the final manufacturing operations, the transformer is enclosed in hi shielded case. Hut even automatic machinery is not infallible. Defects may have crept in despite every precaution. Handling of the coils way huve caused short circuits. The smtomati machinery mav possibly not have, been |>erfectly adjusted. Now the transformer is put through a number of tests before it is accepted for shipment. Ten instruments, directly before tho eye 3 of the inspector and checker indicate bv movements over " small defined range whether or, not a given transformer is good or defective. Two of tho most interesting and valuable lists check tho amplification ratio of the transformer in on amplifying circuit, with a standard valve. Readings are taken at 50 cycles and at ■'■'" cycles, two oxtier- of the range, over which an efficient transformer should perform. If it delivers its rated amplification at these two points, consistent amplification over the entire raime is assured.

Winding two and a half miles of wire finer tlmii a liair is an accomplishment in ilsclf. Now consider what it means to wind 750,000 miles of wire .n year. That's tiio yearly total of a factory producing an average of ICOO transformers a day, and that figure is by no mO4l ns large, because sonn* companies turn out something like 10,000 transformers a day; 3YA Christchurch. It may interest out of town readers, to know that 011 c of tho new steel towers has been completed and rivals the destructor chimney as a prominent landmark. This tower is on top of tho A. R, Harris Co.'s new building. When its mate goes up from the ground level and tho aerial is swung between" them, no city in New Zealand will have anything over Christchurch as far an up-to-date aerial equipment is concerned. Tho same also applies to tho new studio which is now finished. As most listeners-iu have heard, via the ether, he csei.t station will bo closing down for a week to enable tin: change over to he made, and the transmission will then be much improved. Everybody is calling out, especially in tho country districts, for continuation as to advice re. tho correct time. Why was this stopped? Kven in tho town tho advice as to the correct time is much appreciated, and for country listeners it is more than essential. It is to he hoped that the time and tho weather report will I* sent out twice in each transmission. Listeners to 3YA have been treated to some very interesting and welldelivered talks by Mr J. Prentice, and everyone I hare spoken to hopes that Mr Prentice will he stationed permanently in Christchurch. 4YA Dunedin. This station continues to put on some very good programmes, both in quality and • variety, even for the afternoon transmissions. The station manager deserves much credit tor his efforts, and it it: a.great pity that he hasn't a better piant at his disposal. As I have mentioned before, Otago <ind Southland badly need a station at least equal to Christchurch, because dead spots and fading, etc., are very pronounced down there. It would even be a good plan to mstal a small GO-wntt station in lnvereargill, and it i.s to be hoped that this winter improvements will be effected. Efficiency in Set Building. When we consider that the signal energy from fin- distant is often less than a millionth of a volt, it is apparent that a slight resistance, introduced into the receiving circuit will greatly impair or destroy signals. Thus, even though good signals are received and properly amplified from a local station, the same receiver may no', perform at all satisfactorily when receiving distant stations. For example, the more energetic signals from the near-by station will bieak down slight resistances, such as films of oxide or grease, which would interfere with the weak, tang range signals. Hearing m mind the long path of the signal enerirv in its journey from the aerial to the brail phones or loud speakers, and summing up tliu number of joints or connexions it has to cross, it is really surprising that it is ever able to be heard at all. And figuring the tow value at which it starts, wo must appreciate that tho slightest loss seriously affects the .strength of the final signal. The best results requirethat the builder use great care in tho selection of conductors. including aerial, lead-in wire, and internal: study diligently tho lay-out of the set to obtain the" shortest paths possible

for the signals, and use the most painstaking efforts in wiring-up tho set to make all connexions perfect. Avoid leaks due to improper insulations and prevent interference from parallel wires running 100 close together. We have ,)ust learned that Mr J. 1. Stnail, tho Radio Engineer, of Carey's Building. Colombo street, has been appointed Christchurch n-">- ' for tho famous "Grebe" •'i-valve syncopha.se receiver This will prove of special inlerobt to all who want perfect rece|ition. — 6 Ask to hear tho SFERAVOX, the reproducer supreme, and note tho difference in volume and ptirity over tho usual horn type loudspeaker. Tho SFERAVOX is non-direetionaJ and is heard with equal volume from angle.— £5 6s, of all loading radio dealers.—-New Zealand Representatives, Brown and Durcau, Ltd., Wellington. —2