New Points For Listeners and Dealers

Radio Record, Volume I, Issue 37, 30 March 1928, Page 2

New Points For Listeners and Dealers

By

Meter

The aim of this section is to give listeners infarmatiom ef new and interesting devices and sets on the local market. It is free of advertising intent or influence and to the hest of our ability will convey only absolutely reliable statements. Names, prices rine sources of supply are mentioned for the benefit of readers and. to save individual UITye =

N my rounds among the radio traders, 1 have re. ceived unvarying endorsement of my oft-repeated coutentiom that the multi- : my yalve receiving set to: selli in. New Zealand must, under average conditions, be capable of bringing in the chief Australian broadcast stations with ample loudspeaker volume. A receiving set of four or more yalves which cannot accomplish this is bound to. remain in stock. This is a stiff proposition. as compared. with. America, England and the Continent.. In otlrer parts of the world where broadcast listening is popular the radio public are content to reach out, on the average, not more than five or six hundred miles. New Zealand is an insular country with & somewhat restricted population and’ resources for broadcast entertainment, while at a distance of about 1800 miles lies Australia with its, population of six and a quarter millions and broadcast services of an exceptional character, due, of course, to the liberal financial support of the listening public. Now, 1300 miles is a goodly distance to span when entertainment from stations of only ~ 2500 watts aerial power is sought for. This. entertai--nent is demanded nightly,, although . is unreasonable, for, apart from static interference, the natural and unpreventible ‘fading’ under adverse conditions on certain occasions renders absolutely consistent londspeaker reception impossible. However, an efficient multi-valve set can be relied upon to give many programmes from Australia eaclr month. It is doubtful whether any multi-valve. set buyer in New Zealand has yet made his purchase without stipulating tlat the set must "bring in the Australian stations." What would. the Agnerican and English manufacturers say if they were told that every multivalve set they turned out was expected to give fairly consistent loudspeaker reception over a distance of about 1300 miles? Seeing that the majority of buyers -in America do not expect such a performance, it speaks well for the vast majority of imported sets that thev actually do accomplish tls feat fairly regularly. Anyhow, as reception of Australian programmes. is a powerful aid to the popularity of broadcast listening in New Zealand it should. not be discouraged. A £120 ZENITH MODEL. THE extraordinary development of the broadcast receiving set during the past few months is exemplified whereever one goes to see the latest in imported productions. The crude-looking apparatus with several tuning coils is just a memory nowadays, and in its place is the elegant, handsomely finished model, in whieh simplicity in tuning is one of its outstanding features. The prices sometimes, too, have soared, in

keeping: with the many expensive refine~ -ments, and) the superluess of the conisale models. This week I hadi the | pleasure of examining; Zenith Com;pany’s; "Yen, De Luxe’ model’, stacked ‘by Mack’s Radio. Cx,, Ltd, Kent Ter--race, Wellington. ‘This magnificent, com sole set has. five stages of radio-fre-. _queney amplification, a detector, and four stages of audio-frequency amplifieation. The circuit is ane of the Zenith Company’s own design, and, seeing that it is a remarkable long-distance getter,, ‘operated: by only one tuning dial, the makers lave achieved an undoubted triumph. With the one tuning control, 2VA, Wellington, is completely cut out,, and 2FC, Sydney, brought in with full loudspeaker strength, in a city location: So its selectivity is definitely established. The set is thoroughly shielded within, and there is a neatuess about the workmanship whiclr is the ball-mark of superiority. The cabinet is made~locally, and is a replica of the most costly imported: article. ‘The: four audio stages are a combination of transformer and impedance amplification. The tuning Jial is well illuminated with a . little electric bulln The set has a wavelength tuning range from. 80 to 540 metres, and in combination with a short‘ware adanter; can operate down to 10 metres. The set is operated with an external ‘‘A" hattery, fitted .with a trickle-charger, a ‘‘B’’ eliminator, and dry-cell ‘‘C" battery. This De Luxe model sells at £120, complete with all batteries and accessories ready for operatien Mack’s Radio. Co.. also stock other models of the Zenith. including a ‘particularly successful DX performerthe Model II. This. is a 6-valve set, im which every valve works, the Zerith Company having their own valveless ‘method of aerial-counling, so that no loafing valve is required for that purnos¢ There is. a- single-control electric lighted dial, with four condensers pnermanently balanced on one shaft. The set is battery onerated, and it is wired for a power valve in the last audiostage. Rut there is an ample range of Zenith lines, ranging in prices from £36 to £750. THE NEW "SCREENED-GRID" VALVE. (PHE new radio amplifying valve, Radiotron. UX-222, belongs to. the "‘Tetrode" or four electrode class. The Radiotron UN-222 is a four element sereen-grid valve particularly designed for radio frequency aanplification. The experimentally inclined amateur will find that with proper shielding of the radio frequency circuit, neutralising and’ stabilising devices are unnecessary, the introduction of the shielding: ‘‘Screen-grid’? between the usual control or ‘‘Control grid’? and. plate, not only. decreases. plate to grid. feed-back capacity, but also increases ) the mutual conductance of the valve.

: Radiotrom UN-222 may also be used ‘im a totally different: role, as am audio frequency amuplifier, im resistance coupl- | ed, circuits. Higher overall. amplidica- | ‘tiom at audio frequemies; is possible | with this valve without greater plate resistance than that, of three element | higin mu valves. The. filament, of the Radiotron WX-222 | operates at 313: volts, and the filament | consumption is, 132 of am amp, but with a. series resister of 15. olims.,, it can be: connected! in parallel with 5 volt i filaments. CHARACTERISTICS. (When used as a radio frequency am_plifier witln special shielding; ). Type of base, Standard American UX.. Maximum overall height ......... 5gin. ‘Maximum. overall diameter .., t 13/16in. Fil. volts ..... seeeeeeeees aeeeeeeee dew ececeaees 8.3 SRG. current ....cceecceeceeeeee 282 amps. Plate VOlS. o.csesecsrece ereterseerseonee LBB, Grid: volts, inner-grid’ .....cescsceeree EG Grid volts, outer-QrTid. w.ccccccneree 48 15 mfa Plate current .......... coenensocs 1.5 ma A.C, plate resistance .. 850,000 ohms Mutual conductance ........... 850 m/o Amplification factor oc. 300: (When used as an audio frequency Amplifier in resistance coupled’ circuits.) Fil. volts ....... pescseecevaconccsccssvcrses 3.3 Fil. current ...... sacs scence sess 192, amps. Plate volts ........ seseeeessseee 180) | (Applied , plate , coupling resistance of 250,000 ohms. grid volts). Grid volts-Outer-grid ...... ence ceccsoresevccecsioccs™ Le Inner-etid es... PTO reT seuss DBE Plate current ......... seeesesseeeeees 8. mila A.C. plate resistance .. 150,000 obms. Mutual conductance ..... 400 m/o Amplification factor .....sccceeeerseeeeees 60 PROMPT AND GOOD. REPAIRS. A PROMINENT Amxerican. radio service man says:-‘‘The appreciation of an instrument lies in the ability to use and enjoy it. It is evident that no radio set conlé ever be built which would not, at some time or another, require some repairs. When these repairs will be needed is something which cannot be foretold. But the value of ‘the radio set, its prestige and that of the industry, may be greatly strengthened if the service given and the repairs made are of such quality of workmanship and materials that the owner will have confidence in his set. ; "With the keen interest shown in radio, many inventions covering the entire field have been brought out, and it is now possible to determine the trouble in any set with apparent ease. ‘There have been several types of troublefinders placed on the market, and it is an easy matter to build one which will answer the purpose.. The real value licts in using them, and in follow~ ing up the trouble when it has been located, and staying with it until it has beem thoroughly cleared up. "One of the features offered through our service department is same-day. service. If an owner brings in his. set during the day, we are in a position to offer him. immediate attention, and. get it in shape-unless there is some major trouble-so that he can use it that night. We have a complete stock of repair parts on hand, and, with a proper knowledge of construction, it is a simple matter to. rush the order ‘through. "‘Co-operating with this repair service should be an iron-clad ruling that all ‘spare parts and materials used in this. work should be of the best. I doubt if there is anything which will do more harm or will do more to break down ‘e confidence im radio, than for some mechanic with limited abilitv to inject some cheap or used parts into a set which has cost quite a sum of money." TELEVISION RECEIVING SETS, A REPORT of a recent successful test ~ of television was published in the ‘Radio Record" of March ¥. A New York writer says:-‘At last television has become something more than mere theory. Demonstrations in Scheuectady recently prover miost successful, pictures. of announcers were sent through the air, the eventful images being seen in a cabinet. ‘Ihe device is not complicated, and resembles an ordinary broadcast receiver. ‘I'he sets (as reported recently in the ‘Radio. Record’) Were designed and: demonstrated by E [, W. Alexanderson. . Television in the home is an accomplished. fact. It has been done, as a ‘large group of uewspaper men can verify. ‘True, it is only a laboratory development as yet, but 1928 doubtless ‘will see the installation of television transinitters in: more than, one broadcasting station, aud the marketing of television receivers at a price within the reach of the average home. "It is now a problem only of refinement of apparatus, and bringing the cost element down-not so difficult as it may sound-to a conmiercial basis.’’ "Dr, Ernest TF. W. Alexanderson, chief consultiire engineer of the Radio Corporation, and also a consulting en--mireer of the General Iflectric Company,. designed these sets, Dr. Alesanderson, a blocky, square-faced, unassuming: scientist, who disensses 1adio. marvels -witl: a noticeable Swedish aceent, insists. that his, work involves no new principles. It is a simplified applica~ ‘tion, he says, of principles previously known atd founded upon the contribu‘tiens of many pioneers. ‘If you loolt into the cabinet at the heart of this wonder the gp eomoed impression is surprise at the absence ef a complicaind collection of gadgets

and! electrical whatnots. Wow see scarcely apparatus more thaw, is found! im a. good cemimercial broadcast receiver, There is nothing inkercmtly expensive ‘about it. A. reasomaible: guess is; that it could be sold! im volume for araund 200, dollars: | Real Motion. Pictures. "The human eyz holds: an inypressiom -one-sixteem of a second. If yarying: impressions, are conveyed to the eye att the rate of sixteen individual impres~ -sious or more per second, the result is a moving picture. Each impression .is made up of light and dark suadings. Whe: a face is broadcast by television ‘its lights and shadows have to be trans‘lated! at the transmitting apparatus in ‘terms: of electrical impulses. This has ‘to be done on an instalnient plan, shipping one small square of the face at a time. A moving bean: of light. is ‘played upon the face through a spinning | .dise,, which has. holes, punched into. it. What is glimpsed through each hole is a separate unit of the image. "The vatiations of the ght beam, as caused by the varied shadings of the face, are translated into electrie current ‘througlr the now familiar plioto-electric: cell. Thus, the image takes the air. Its wave impulses are picked up by the receiver as in the case of sound and. are emplified, as is, sound! by a loud‘speaker. The impulses next travel toand vary the intensity of-a neon lamp. No screen is used. By increasing the number of holes in the disc, a more clearly defined image wilh be oabtaine:d: in the sets of the future, and images far larger than three inches square will be. possible. . "There are two alternatives to the spiuning dise-a mirror drum or a disc with lenses. "The spinning disc is used by Alexanderson because holes eest less than mirrors or lenses." THE BROWNING-DRAKE, CLIRCULET. "RHE, old. three-coit regenerative set received its. hardest knock probe. ably from the Browning-Drake circuit.. This is as- it should be, for the old so-called ‘Armstrong’ (rightly De Forest ‘‘feed-back"’) circuit, if careless‘ly or stupidly handled, is one of the most vociferous "howlers’’ yet devised by radio inventors. But there is. al‘ways this much to be said in favour of the three-coil regenerative circuit, owing to its reaction it is a great dis-tauce-getter and has many wonderful performances to its. credit. Ik was a set of this type which first brought KGO, Oakland, California, in to Wellingtom on the loudspeaker, and a similar set. was second to accomplish this feat, both outfits having only three valves. This performance took place some four years ago, and power valves were uot the vogue in those days. But the old three-coil set had to go, It was a disturber of the ether and, although a fair proportion, unfortunately, stilt linger with us, some hundreds of listeners have scrapped them or altered their three-coil cirenits into more modern circuits. ‘lhe first es. sential was a set that would not ‘‘howl" and which had reaction, if the threecoil circuit was to: be supplanted. The next requisite wss a set which was easy to build and easy to operate. Now, if a Browning-Drake circuit is correctly, neutralised, it is as silent as the tomb, despite how carelessly .you operate it. ‘The reaction of the Browuing-Drake is one of its distinctive features, It is not so difficult to build as a three-coil set, and it is incomparably easier to. operate. Another factor which places the Brown-ing-Drake far ahead of three-coil circuit is: that its one stage of radio-fre-quency amplification is considerably more efficient than, any known. means of adding a stage of radio-frequency ‘to. the three-coil circuit. The ordinary Browning-Drake set excels in longdistance performances with only four valves, so that it is not substantially more expensive to construct tham the |

thyee-eoil cixcnit. Then, the Austral. lam stations, excepting only GWE, -- ‘Penth, all hadi their wavelengths res’ ‘duced to helow 550° metres, ‘This: ‘tobbed the tlhiee-coih set, with its: . ‘hamd'y plug-im coils to adapt it to any ~ , Wavelength, off one of its; gneatest res. The Browning-Drake circuit cam take in all the wavelengtlis: commonly used by the broadeast sta- , Ustemens. So now, like: Othello, its: )eccpation gone, there is no particular: K. Fear, of Fear and Co., Willis Street, Wellington, {nformed me the other day that he is working at full pressure: to cope with the demand for the conversion of obsolete sets into Browning= ) Drake circuits. Mr. Fear has made a special study. of this. circuit and is, a regular encyclopaedia on it. He: builds the Browning-Drake regenera» formers and aerial tuning coils for standard new sets, or to match cus tomers’ own condensers and valves, He also finds a constant demand for , correct neutralising of clients? ihome-builti sets, and he does this for "2, 4 and 5-volt valves. There is not. a little skill required to neutralise the Browning-Drake circuit, and many block. The correct neutralisation of the Browning-Drake circuit is essential to obtain the best results, not to mention the desirability of preventing it ‘from being an even more ferocious ‘"howler’" than the obsolete three-coit "regenerative set. TEST YOUR VALVES. ft is a good’ plan to have the valves. in a receiver tested after every. three or faur hundred hours of service. If a receiver is in use an average of three hours per night for instance, it will be worth while to have a service "man test the valves about once every four months, and to replace any that are found te be wearing out. This is particularly important where the receiver makes: use of rheostats for the adjustment of the valve filament. supply, because if a single valve starts to: wear out there will be a tendeney to. make up the decreasing volume by home-builders find this a stumbling1O\ : petemqeate- TE: tions. naw, available to Wew Zealand reason why the three-coili regenerative " Cixenit should continue: to exist, One " of Wellington’s leading authorities om ° the Browning-Drake circuit, Mr. C. G.. 5 ‘turning the other valves up higher, and the usual result is: that several valves: are prematurely worn. out. Replace- ment of the one poor valve would save the others.