New Points For Listeners and Dealers

Radio Record, Volume I, Issue 43, 11 May 1928, Page 2

New Points For Listeners and Dealers

"m By

Meter

_ The aim of this section is to give listeners information of new and interesting 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 and sources of supply are mentioned for the benefit of readers and to save individual {nguiry

HROUGH the courtesy of the General Electric Co., Ltd., Empire Chambers, Willeston Street, Welsate: : lington, I have been able fitinastied. to put the Gecoplone gramophone electric pick-up througha series of tests. this is an English line retailed at only £3--a low price for this type of device The pickup is slipped on to the tone arm of gramophone and an eleven-foot cord is plugged in to the detector valve socket. The radio loudspeaker is then plugged into the last stage of andio of the radio set in the ordinary way, so that the record is reproduced from the loudspeaker. The Gecophone pick-up was put on test with various types of gramophone records and gave good volume without any tendency to chatter It does not weigh so heavily on the records as some types of pickups. The design is neat and compact and the material is good. STOCKS ARE SHORT. QVER-CAUTIOUSNESS in buying is almost as unprofitable as reckless buying on the part of the radio importer. ‘‘Meter" has seen some adniirable lines imported within the past few months which were cleared out immediately. These lines eomprised ouly a few samples, and they came from manufacturers of high repute, and as the merit and prices of the lines were "right" according to information ‘received prior to importation it shows over-cautionsness in sending for only a small initial supply of the lines Anyone who has his finger on the pulse of the New Zealand trade knows = imuvediately what will sell Radio listeners are notoriously impatieut, and if the line they want is not availakle they are. easily diverted to something else. This | means that what is one importer’s Joss is another’s gain, but one, ucvertheless, regrets that a market for better goods, which means greater satisfaction for the buyer and a better advertisement for broadcast listeninz, is sometimes lost through timidity on the part of an importer or his foreien buver ‘‘Meter? knows of lines which will sell promptly on sight, ard is surprised to see ouly a small initial consignment arrive from the manufacturers, bat he was not surnriced tr

see the line cleaned out within a few days Vse better judgment, gentile. men! WILL PRICES DROP? OT infrequently the excuse given by people with means for no. possessing a receiving set is that they are ‘"‘waiting for prices to drop, as they surely will in the near future," or words to that effect. If we are to be guided by the latest news from the United States prices for scts and components are not only unlikely to drop, but are ou the up grade. As a matter of fact some of the makers of the best receiving sets in the United States increased their prices on Vebruary 20 of this year. ake the ©. R Lenz Co., Long Island City, New York, as an "example On February 20 that company increased the prices of their sets by 33 1-3 per cent., and the prices of their B and C eliminators by over 14 per cent. A nrniber 0. other companies also announce in creases all round. The new refinements in radio sets cost money and are not calculated to mean lower cost to the public. The indications are that prices will be steady tur a while now, but there are no prospects of a reduction in the prices or the better class of sets & NEW POWER AMPLIFIER VALVE. "THE CX-850, UX-250 is a new valve for use in the last stage of a transforiner-coupled audio frequency amplifier For the same filament current and plate voltage it has more than twice the undistorted power output of the 210 valve, which thus adapts it for use with loudspeakers to be used in large auditoriums. Dune to its low plate impedance it must be used with an outprt transformer or choke coil and bypass condenser. Its filament current is 1.25 amperes at 73. volts, the filament being of the ed ribbon type. It has a height of 64in. and a diameter of 2 11-16in., fiiting a large standard socket. Its characteristics at various plate voltages are as follow :- | Plate voltage 250 300 350 400 450, Negative grid , Wias {volts} 45 54 63 70 = 84

Plate current (milliamps) 28 35 45 55 55 Plate resistance {it.c.} (olims) 2100 2900 1909 1809 1809 Mutual — conductazce (inicrohins) 1800 1900 2030 2100 2100 Voltage ampiification factor si... 38 3.8 38 38 3.8 Max nnidisforied = ote put (milkyatts) ..... 900 1500 2350 3250 4650 . The new yalve’s maximum output is about #4 times that of a UX-201A valye This valve, which is for use with an A battery or eliminator, is not in New Zealand yet. REMOVE SURPLUS FLUX. [ a very few weeks the cold -erisp nights that every radio fan has heen waiting for will be here. When this time arrives you want to have your set in the most efficient condition possible. Now is the time to overhaul your set so_that when real DX weather arrives you will be able to pull in distant stations, If you are building a new set take special precautions in the soldering of all joints, and be sure to clean off the surplus flux with an old tooth brush or a bit of cloth moistened in alcohol lux between two joints will allow the eurrents to leak across and lower the working ability of your receiver If your set is an old oue the probabilities are that a nuinher of connections are badly correded or coated with dust. This may be due to a coatine of excess flux that was left after the connection was soldered. Go over every connection as described above and vour reception may he greatly increased If rosin flux was used there will be no need for the above cleaning process, because rosin is an insulator and will not cause this sort of trouble. THE SHIELDED GRID VALVE. RY OST favoutable reports have been received from those whe have installed the new shielded grid type of valyes in their receivers, the valves, alihongh more expensive than ordinary

valves, are weil worth using It is’ found that when they are employed as radio frequency amplifying valves, a degrée of sensitivity seldom obtained with thiee ordinary radio frequency stages is easily obtained, Although the valve is remarkably stable and easily controlled, interference from atmospherics 18 said to be greatly reduced. Used in short-wave sets, the valves are giying striking results, and seem to make am ideal addition for the reception of short-wave overseas broadcasting. The sets are comparatively easily made, and ordinary circuits can be modified to receive them, It should be borne in mind, however, that careful shielding of the apparatus in the receiver is essential ta successful operation, The screened rid valve must be shielded in a special metal case, and the radto frequency and ‘detector tuning circuits should also be separately shicided' for best results. "+h a little care, however, no difficulty will be experienced in carrying cut the shielding work. An aluminium panel instead of an ebonite one will be found useful, and the remaining shields can ‘Se mrade from sheet aluminium or sheet copper. Copper will probably be found slightly easier to use than aluminium, as it ean be soldered without diffienlty, If aluminium is used, the pieces of the shiclds may he bolted together with small brass bolts of the kind widely used for wireless terminals, CORRECT GRIN LEAK. GET builders will find that the simplest method of adjusting the grid-leak of the detector valve is to try successiveiy grid leaks of different values until the one which gives the best result ‘s found. Assuming the use of a .00025 microfarad fixed condenser as grid condenser, most of the detecting valves usually work most satisfactorily with a grid leak having a resistance of about wo imegohms. Occasionally, however, cases will be found in which this valne is too hight, and a tendency for the set to howl develops until a leak of lower resistance is used. Jt should he borne in mind that the position of the grid Teak return on the filament is of as great importance on the detector valve as it is on an amplifier. It is usual now to connect the grid leak across the grid condenser. When this is done,

the second end of the tuning coil, which 1s connected to the grid condenser, becomes the return lead for the grid leak, This return should generally be ‘connected to the positive side of the filament, but cases will be found in which it will give best results when connected to the negative side of the filament of che detecting valve. When making a new set, it is therefore wise to make this return connection of a temporary nature, until 1t can be ascertained by test whether it will give best results on the positive or the negative side of the detector. It should be borne in mind, also, that the value of the grid leak for the best operation of the set will depend, to a considerable extent, on the pressure used on the plate of the detecting vaive. Adjustments to the plate pressure of the detector valve will often greatly improve both the quality of reproduction of a receiver, and also its sensitivity. NEW ENGLISH VALVE. f NIEW receiving valve just announe. ed by a British manufacturer incorporates two useful features, which will appeal to many listeners, The main nurpose in designing the valve was to have an instrument which would work from both a two-volt and a four-volt battery. Incidentally, the type of construction adopted virtually gives the valve two filaments, so that when one is burned out or broken, it can still be nsed for a time. Although not absointely new, the internal construction is unusual. The valve reallv contains two filaments, two grids. and two plates. ‘© two grids are connected, and so are the two plates, so that they really work as if thev were onlv one large grid and one large plate. ‘I'he two filaments are connected at one end, and ‘he free end of each is bronght through the glass in the form of a lead. A lead through the glass also provides contection to the ends of the filaments ioired torcther. If it is desired to use the valve from a four-volt battery, the filaments are used connected in series. If onlv a two-volt battery is available, they ean be connected in parallel. If one filament Lurus ont, the other can still he used from a two-volt battery.