New Points For Listeners and Dealers

Radio Record, Volume I, Issue 37, 6 April 1928, Page 2

New Points For Listeners and Dealers

By

Meter

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

m I was the dream of us broadcast listeners half a decade ago that in some dim and distant day, we would have radio sets Meme) which would be operated solely by plugging in to the house-light-ing electric current. This we regarded as a distinct step towards the wireless mienmum, hut the thing sounded SO. wildly improbable in those days that the subject was never seriously discussed. But our dreams have come true, for a few days ago I had the infinite pleasure of operating and testing exhaustively a seven-valve neutrodyne, which operated solely from the houselighting circuit, This, I understand, is the first electric socket set landed in Wellington. There is no battery at all, either "A" or "B,’’ even the lighting of the valves being -accomplished by the honse-lighting circuit without trickle-chargetrs or separate eliminators. Evervthing is enclosed within the set, and it is so compact that I was able to catrv it in my arms. The only thing necessary to "crank up" the set is to Plug the attached cord-end into the lighting socket. All this seems unbelievable, but ‘‘facts is facts.’"? The set under review is the new Freed-Eise- mann, Model NR-60, Flectric Neutrodvne, for use with 250 volt, 50 to 60 cycle, alternating’ current supply. Through the courtesy of Messrs. Preston Billing, Ltd., I was enabled to test out this latest wonder on my own aerial. The set is enclosed in a luxurious walnut cabinet 10 inches in height, 223 inches in length, and 16 inches from front to back. It is fitted with four **326,"? one ‘827,’ and one "871" valve. There is also one ‘380’ rectifier tube. There are three stages of radio, one detector, ont audio valve, and one power valve. The walnut front panel bears a massive, gilt shield, through an aperture of which appears a sector, of the tuning. calibrated dial, electrically illuminated from within. There ‘are only three knobs to handle-a volume control, a knob for the single tuning dial, and a knob for vernier tuning. The tuning is the acme of simplicity. The electric current is switched on or off by a small brass handle protruding through the volume control. On raising the lid all that meets the eve inside the cabinet are the valves and gilt, metal shielding, no wiring being visible. The temperature of the valves is constant at the highest peak of efficicney; there are no rheostats. The control of volume is effected by the operation of a powerful resistance inside the set between the aerial and earth circuits. If the resistance is decreased portion of the radio frequency current entering the set from the aerial is permitted to flow to the earth lead without passing throueh the valves. At the rear of the cabinet is a face, safety fuse container. A spare

neat screw-in type, porcelain with mica goes with the set. Only one jack is provided, and there is a loudspeaker filter nnit embodied in the set, so that there is no question of contecting the loudspeaker cords with wrong polarity. I was reguested by Mr. Preston Billing to test out the set for several nights. During the first two hours I brought in fourteen New Zealand and Australian statious with good loudspeaker volume; indeed, the tremendous volume of the chief Anstralian stations was unbearable, so that I had to reduce the volume control to half. The overhead tramway wires run alinost parallel with my aerial, at a distance of about 120 yards, and after exhaustive testing I have not been able to detect the slightest electrical noise from passing trams. This is most comforting to a_ city dweller, for tramcars are frequently spoilers of radio reception. I found at first that my 145ft. aerial and lead-in gave me broader tuning than is desirable, so that 2YA, Wellington, distanced oniy half a mile, was spreading over the dial. Next day I lopped twenty feet off my aerial, and the remarkable | selectivity of the set became manifest, for I had no difficulty in silencing the "‘loud-voice" to hear 2BL, Sydney, although my aerial is so close to the Mount Victoria station. My aerial is now 125 feet in length, which is stil} about 25 to 65 feet too long, according to the instructions which accompany the set. Now, just a word about tone. There is no complete enjovinent, to the musically inclined, without natural tone, and in this attribute the set, connected to an Amplion R23 loudspeaker, gave the utmost pleasure GRAMOPHONE PICK-UP, TPHR Gramophone ‘*Pick-up" is an electro-magnetic device by which the sound vibrations recorded on a gramophone record can be converted into electrical impulses. I‘hese electrical impulses are exactly sitilar to those given by an ordinary crystal receiver, and in the same way can be made andible by means of a pair of telephones connected across the terminals on the instrument. If, instead of connecting a pair of telephones across the ‘pick-up’? we connect the terminals direct to the gridfilament terminals of a low frequency valve amplifier, we can obtain sufficient energy to operate the largest type of loudspeaker. With a properly designed amplifier and londspeaker, the results obtained are superior to the ordinary gramophone, not only with regard to strength, but also as regards quality. There are manv occasions on which it is desired to obtain more volume than can he. obtained from the ordinary gramophone, and when a band ot orchestra wonld not be available. or wonld he inconvenient. On such seensions this device, with a suiinhte =

amplifier and loudspeaker, can be utilised to take the place of the band for the largest dance room or hall, also at garden fetes, entertainments, sports meetings, bazaars, etc, The "pick-up" device is usually designed to fit on the gramophone tonearm in place of the sound box. A needle of the ordinary type is fitted in the "pick-up" in exactly the same -way as in the sound box, and, if not of a special type, of course requires changing after each record. THE NEW VALVE. T the present stage the constructor is probably mire interested in what the new shielded grid valve does rather than in how it loes it (says a Melbourne writer), so ior the purposes of this article we may skip most of the underlying theory, and content ourselves with the observation that the two outstanding advantages of these valves are, firstly, the almost complete elimination of inter-electrode capacity, thus removing the necessity -for neuttalisation, and secondlv, the remarkably high amplification factor. This .varies from 100 to 250, according to tvpe and condi. tions of use, enabling an actual radio frequency yoltagve amplification of from .80 to 50 per stage to be obtained with comparative ease. The internal feedback which in a normal valve causes instability, and has to he neutralised. is caused by the capacity hetween the plate and grid and their respective connecting wires. This capacity cannot be wholly eliminated, ba‘. as is well known, wher capacity coupline exists between any two bodies. it can he eliminated bv internosing between the bodies a sufFciently large metallic shield, which is then earthed. This is what has been done in the screened wtid valve. Bv carefully designing the valve so that the grid and plate leads leave the valve at opposite ends of the tluss bulb. the capacity is reduced to that existing between the grid and vlate. ‘These are screened from each other by interposing a screen of wire mesh resembling a second grid. This erid is earthed thronvh its batterv. Having thus practically eliminated coupling in the valve itseif, it becomes all the mote necessary earefully to. eliminate all couplings between the coils, condensers, and other apparatus comprising the grid and plate circuits, and to prevent back coupling through hatteries and tsads. Yo this end the respective circuits must be completely screened from one another by metallic screening hoxes as well as to use bypass condensers and cliokes in the bat tery leads. With all precantions a certain amount of back-coupling remains. hut provided it is not attempted to chrr --te

tain amplification in excess of 905 to 40 per stage, and consiruction is carefully done, there will pe no instability. Now for results. It will be found that the use of a short wave radio frequency amplifier employing one of the new shield grid valves opens up a tremetidous new field, particularly in the direction of long distance short wave broadcasting. Tests conducted by the writer on the Siberian broadcaster RFN gave an idea of what might be expected with a properly-bnilt amplifier unit. rhe station was very weak during the tests, being only R4-5, and with a standard detector audio receiver very diffisult to tune in. On connecting the R.F. amplifier the signal strength went up to R8-3, u truly remarkable merease. More important was the ease with which the station could be tuned in ‘There was no need to "joey" the detector circuit by increasing the regenera‘ion to a point where the set oscillated The tuning resolved itself into the easv attair of the broadcast receiver. Tests m weak code stations proveé the efficacy of the unit as a D.X. getter Stations which were so weak as to be below the noise level of the -eceiver "hen the detector audio arrangement Was used could be brouxzht np to suffi sient strength to be clearly heard. There is no doubt that for the experimenter the UX222 and similar screened grid valves offers a wide field for investigation. As yet the average radio enthusiast knows but iittle about the new valve, and in this article only tle fringe of its operation has been touched. However, as experiments reveal further facts about its operations these will be made available. In any case, the points touched uposi in the preceding article should help those who wish to experiment with the new valves as radio frequency aniplifiers on wave lengths below 100 metres SIX:VALVE PORTABLE SET. ‘THROUGH the courtesy of the Amalgamated Wireless (Australasia), Limited, I was able to test out one of their six-valve portable receiving sets under c¥itical conditions on-a recent afternoon. The set in question is the Radio Corporation of America’s Radiola No. 26, a compact little six-valve superhetrodyne Wo larger than the case which contains the average office typewriter. ‘The rotatable loop aerial forms portion of the hinged door of the cabinet, and a sweet-toned loudspeaker is built into the set. The valves used were Radiotron UX199’s, operated by dry-bat-teries contained in the cabinet. © The cabinet is of mahogany, atid "is fitted with a solid leather handle. For home use with an outdoor aerial, an antennacoupler is provided, and the set is permitted by the P. and T. Department for use in this wav. An extra bat-

tery-box and large-sized batteries for use at home are included with the set. The set has only two tuning controls, and requires no previous experience to operate it. ‘There are innumerable listeners who have their motorcars, launches, or ‘"‘batches,’? who desire a receiving set they can easily transport. It is specially for this class of listener that the Radiola No. 26 is designed. ‘The writer took one of these sets by motor-car considerable distances around Wellington, and good loudspeaker volume from 2YA was obtainable all the while, even: when the motor-car was moving fast. A home test showed that the Radiola No. 26 is also a first-class performer on an outdoor aerial, bringing in the New Zealand and Australian stations splendidly on the loudspeaker. For" portable purposes, the set weighs 40]b. complete with batteries and valves. With an antenna coupler for use with an outdoor aerial, and extra battery-box with large-sized batteries, tm addition to the portable batteries, the set is retailing at £60 complete. TONE, NOT VOLUME, "Mr. C. C. KE. Fear, of Messrs. Fear and Co., Willis Street, Wellington, remarks on the subject of londspeakers :-- Now that radio is recognis*S as a necessity in evrey home, it has been noticeable of late that the public are on the search for better reception; that is, improvement in toue, volume apparently being of secondary importance. During the rush of last spring, shortly after 2YA opened up, we sold a great number of speakers, the majority of which were of the cheap variety. Listeners did not seem to worry much about tone; volume was demanded, and, also, it must not cost too much. Now, however, we find the demand is for quality, not guantity, and it must be perfectly natural-no noisy background resembling the scratch of a needle on an old gramophone record. The full range of the human voice or any musical instrument must be reproduced with perfect tone and clarity-not a jarring note in the whole scale. ‘hese desirable qualities cannot be obtained on a cheap speaker, as many people have found to their sorrow, and there is no question about it, the B.C... have lost many a 80s. through a cheap and nasty noise producer. We now find the demand is for the large type horn speakers, such as the Amplion AR19, B.T.H., and Ethervox, as these models have a good unit and a large flare, and therefore are able to give good tone over the whole musical range, together with volume. The speaker unit is also in good demand, as these can be attached to the tone arm of a gramophone and give excellent results. Although costing anything from 17s. 6d. to 80s., the price of a cheap speaker, the results in many cases are equal to a speaker costing anything from £5 to £7.