WIRELESS NEWS.

Press, Volume LXII, Issue 18668, 17 April 1926, Page 8

WIRELESS NEWS.

RESISTANCE COUPLED. AMPLIFICATION. (SKCUIXT WRITTEN »B "THE PUSS.") (By ''Electra.") That resistance amplification has come to stay there can be no doubt. This is quite apparent, judging by the number of manufacturers employing tins method of amplification in their receivers for the forthcoming season. Too long has the radio manufacturer neglected the subject of quality amplification This may be readily understood when wo consider that for the past three vears volume has been the sole aim in'loud speaker reproduction. Quality has been neglected. . With the present day trend in dcsi«n. to attain perfect reproduction ot music and'speech, theie have been many radical changes in the design ot loud speakers and amplifiers. ine majority of changes on the amplifier side have been in the improvement ot transformers to a limited degree, since it is common knowledge that the audio frequency transformer possesses many inherent disadvantages not conducive to the perfect reproduction of music and speech, such as is encountered in everyday broadcasting. Good Reproduction. With the present-day advancements in the design of cone type loud speakers, there is no reason why excellent reproduction of broadcasting should not be obtained, provided one uses a suitably designed amplifier. Here it may be emphasised that the only distortionless method of amplification, or, to be more correct, the nearest to distortionless amplification is that obtained through a well-designed resistance amplifier. The radio fan might ask: How is it that resistance amplification did not hold its own with the transformer when broadcasting was first announced ? This will be answered in the following paragraphs. In the early days of radio broadcasting the sole aim of the designer of radio apparatus was to the greatest amplification possible with the minimum number of tunes. To-day the tendency is to obtain distortionless amplification irrespective of the number of tubes used. It may be safely said that the year 1925 has seen some radical changes in audio frequency amplifiers, inasmuch as resistance amplification gained ground rapidly. This really onlv anplios to the American radio market. Let us turn and see.to -what extent resistance amplification is used in England. Resistance Amplifier. The resistance amplifier, it might be said, was fostered and brought to a great stage of perfection in England, where it is to-day in extensive use, both as applied to reception and transmission in radio broadcasting. It was realised very early by prominent engineers in Great Britain that to obtain really good broadcasting, the transmission of programmes must first be made perfect. We can easily understand, therefore, wny the majority of the European transmitting stations employ resistance amplification in their speech amplifiers. Turning to receivers, resistance amplification was. to say the-least, the •first method used to amplify at radio frequencies; and to the man who really cared about the results obtained in reception, this method of amplification immediately found a place in his heart, not to he displaced later by the transformer, which suddenly' made a bounce upon the English radio market. Of course, so far as the amateur or "ham" was concerned, resistance coupling meant little or nothing; but with broadcasting stations springing up all over the country, radio manufacturers took notice' of the demands of the public, since it was generally recognised that the average radio set was not even on a par with a poor phonograph. To'day we see the greatest manufacturer of phonographs in the world turning to radio as an aid to the improvement of his products. Buch is tho trend of the public demand to-day./ Perhaps the first use of the resistance amplifier was its application as /an amplifier on the ordinary telephone line, since before the ''vacuum tube ' made radio possible, it will be remembered that telephone communication could he made only over fairly short distances. Many of the European telephone companies installed what are known as "repeater" systems to amplify the voice after travelling many miles of wire. This was undoubtedly the true birth of resistance Amplification, to be fostered by tho amateur and brought to itß present day stage of perfection by the radio-engineer. ' Authoritative Opinion. The greatest authority, on radio broadcast mattera in England was once heard to say, "Personally, I always use resistance amplification." This by the way, was Captain E.<.P..Eckersley, the, chief engineer of the British Broadcasting Company. Needless to say, he was' not the only authority who recognised the importance of/this, particular phase of audo frequency amplification. In ita early days, with the very early type vacuum tubes, resistance amplification was considered a subject for the expert only, since the amplification obtainable was not equal to that of a transformer coupled amplifier. To-day, we see tubeß . on the market which are made expressly for use in resistance amplifiers. By the use of such tubes, is is possible to obtain almost as much amplification, tube for tube, as with a very good transformer, not to speak of the increase in the quality of reproduction through the use of the resistance method. It was not until after broadcasting was an established thing in America that the American radio pub-

lie • realised the enormous advantage resistance amplification offered over other methods. Gradually the American fan gave serious thought to his loud speaker quality. This was the first thing considered by the English fan in preference to volume. The King's Wireless Set. Perhaps the best criterion that the resistance amplifier enjoys in Great Britain is that the set used by the King emplovs , resistance amplification throughout, both in the radio frequency, and the audio frequency Bides. Of course, it is understood that such a *et must emplov only the best materials and be designed by the best engineers available. It is amusing to regard the evolution of the resistance amplifier retrospectivelv. In 1917 an experimental resistance amplifier utilised slnte pencils for risisters and grid leaks. The coupling condensers were of an unknown "capacity. No one knew any more about this subject than anyone else; consequently all had the same start. Needless to say. the results obtained even at such a primitive stace, were trulv gratifying. Gradually the onaineer and the mathematician took rhe~ situation in hand, and develnned what we mnv call the ptrfer-t arnnli'fier. for tl'«> rosistarce nWhnrl certainly has prior claim to that distinction. Australian "A" and "B" Class Broadcasting Stations. New South Wales:— Class Meters \\ atts

Transmission Schedule. The following times may be taken as a guide for tuning-in on ordinary week days, but are subject to slight changes on Saturdays and Sundays. Times are given in New Zealand mean-time. 2FC—11.45 a.m.-1.0 p.m., 2.0-8.30 p.m., . 4.30-6 p.m., 8.0-9.0 p.m., 9.2512.0 p.m. 2BL— 8.30-10.30 a.m., 12.0-1.15 p.m., 1.30-3.30 p.m., 4.30-, 8.0-9.15 •' p.m., 9.30 p.m. SIX)— I.3O-3.30 p.m., 4.30-7.15 p.m., 7.30 p.m., 9.30 p.m.-12.30 a.m. BAR—I.3O-3.30 p.m., 4.30-6.30 p.m., 7.45 p.m.-12.30 a.m. 501—10-2.0 p.m., 5.0-6 pin., 9.0 p.m., 10.0-12.0 p.m. 6WF—4.O-0.0 p.m. 7.0-8.0. p.m., 10,95, 11.12 p.m., 11.30 p.m.-1.30 a.m. 7ZL—12.30-1.30 p.m., 4.30-5.30 p.m., 8.30-9.30 p.m., 9.30-11.30 p.m. The above is the. first complete list of Australian broadcasting stations with their wave-length, power, times of transmission (in N.Z. time) to be published. Cut this out and keep far reference.

■JUL Broadcasters, Ltd. (Sydney) A 353 loOO 2FC 1*aimer and Co. Ltd., Sydney ... A 11C0 5C00 2DH H. A. Douglas, Newcastle B 28S 1C0 2UE Electric Utilities Co., Randwick ... B 297 2C0 2BE Bnrgin Elect. Co. , Svdnev B • 326 100 2UW Otto Sandei, Bellvne Hill B 233 oO'J 2K.Y Trades and Labour Council, Svdnev B 280 1500 2MK Mockler Bros., Batburst B 275 2C0 Victoria:— SLO Broadcasting Co. ' of Australia, Melbourne A 371 5C00 3AR Associated Radio Co. of Australia, Melbourne A 4S4 16C0 3UZ 0. J. Nilsen and Co., Melbourne ... B -319 100 3E0 R. J. Egge, , Mildiira B 2SG 1C0 Queensland: — 4QG Queensland Government, Brisbane A. 38-5 5000 4MB 'Radio Mfgs., Ltd.. Brisbane. B 337 210 4IIN Queensland Government, Kockhampton * B 323 500 4CM Dr. V; McDowell, Brisbane B 278 ' 250 4GB Gold Radio Elec, Toowoomba B 294 1C0 South Australia: — oCL Central Broadcasters, Ltd., Adelaide - A ,395 5000 5DN 5DN Proprietary Ltd., Parksifle B 313 SCO Western Australia:— 6WF Westralian . Farmers, Ltd., Perth • ... A 1250 5000 Tasmania: — 7ZL Associated Radio Co., Ltd., Hobart A 417 3000 7BN Tas. Radio Pty., Ltd.', Launceston B 283 250 "A** Class Stations,