WIRELESS NOTES

Nelson Evening Mail, Volume LXIV, 14 June 1930, Page 9

WIRELESS NOTES

GENERAL RADIO NEWS PENTODES? There is no question but what wo will have live-element tubes this year (writes Arthur 11. Lynch, editor of the “Radio News”). The Pentode, as it is called, is a sort of glorified screen-grid tube. It will enable us to secure high amplification and increased power output at the same time. At least these are sonic of the claims being made for it. Every so often the radio business suffers a revolution. This revolution generally occurs at about the time manufacturers are heavily laclen with inventories of receivers in which the revolutionary devices are not incorporated. When the screen-grid tube was introduced many manufacturers had rather heavy inventories, and, in addition, had done most of the engineering work on tlieir advance models for the coming year. A great many of them discarded ail their past work and made

all sorts of engineering compromiscs.nl order to swim with the tide and provide a screen-grid receiver for tlieir dealers. The result of the stampede was tho construction of a group of screen-grid receivers designed in haste, the production of screen-grid tubes designed in haste, and a most unsatisfactory merchandising situation. That the screen-grid tube was an absolute essential for any receiver that would enjoy ready sale was completely disproved by. tlic tremendous sale of two particular makes of receivers, oije of which has sold more without screen-grid tubes than the combined sale of all the screen-grid receivers.

The shrinkage (loss in process of manufacture) of screen-grid tubes is very. high. There are comparatively few which actually measure up to tlu; wonderful qualifications first claimed for them. Tube manufacturers agree that manufacturing difficulties increase about as the square of the number of tube elements. Tho average shrinkage in a good plant making screen-grid tubes is about 50 per cent. According to sound engineering estimates, then, the pentode will greatly increase tho shrinkage. There are at present many very satisfactory radio receivers. They are sensitive, selective and produce extremely fine tone quality. They may be operated for approximately one cent an hour and their original price is very very low. It is rather difficult to conceive of the pentode so greatly improving any, of them as to make it necessary for manufacturers to abandon completely the manufacture and sale of present models even if the tone quality was as. good, and we have yet to hear a pentode receiver capable of the tone fidelity or in any other way the equal of good receivers with standard tubes.

Furthermore, the impression that the pentode is a new tube is completely erroneous. Pentodes have been in use in. Europe for more than five years. They have not revolutionised the radio receiver business there, and t abroad there is a much greater tendency toward 'economy in receiver design than there is here. The vacuum tube is generally recognised as the heart of the radio receiver, and it is apparent that a tube company announcing a new and revolutionary tube would be able to exploit an unknowing public by floating a stock issue on the strength of cleverly trumped-up .propaganda. ; There is no doubt but that there are many fields in which this tube can oc employed to advantage. For instance, a suitable pentode used for the power output in ; automobile radio receivers would enable us to secure satisfactory volume without having to resort to particularly high plate voltage. There are, however, certain characteristics in connection with the development of pentodes which must be overcome before the tube will be satisfactory for home or mobile use. In some of the models of American manufacture which we have seen, the elements are extremely close together. ,In fact, in one tube where a ribbon flamant was employed,, the ribbon had to be placed'on edge to prevent its striking one of. the grids. Such a tube would hardly be useful in ail automobile, or a motorboat or in an airplane, even though, theoretically, it would reduce the number of tubes in the receiver:

It is our purpose to gather as much information as we can concerning pentodes, and to convey this information to our readers. We are at present cooperating with a number of tube manufacturers in making a survey of the possible production of pentodes and their actual application. Official Listener Mr H. Askew, manager of Messrs Wilkins, and Field’s wireless departments has been appointed the official ;listener for Nelson by the New Zealand Broadcasting Company.

The Europa’s Wireless The new North German Lloyd liner Europa is equipped with the most mod'ern wireless apparatus. It permits permanent use of three lines in duplex, which means that messages can be sent as well as received on all three lines at the same time. The transmitter does not affect the receiver, although it is installed directly alongside it in the same room and the aerials are fastened to the same masts. This duplex system is especially notable for its long wave traffic; as the transmission wave length differs only' a, few per cent, from the receiving wave length. Six Radio telegraphists are necessary to work this apparatus. The radio equipment, which was supplied by the Telefunken Company, consists of a transmitting and a receiving section. There is a chief transmitter operating on long waves and destined for direct communication with both continents from any point between the coasts. Its range is from 500-5000 metres, and provision is made for highspeed transmissions. An auxiliary transmitter operates on the usual wave band (580-830 metres) reserved for shipping purposes and destined for communication with coastal stations and other ships. A short-wave transmitter provides for telegraphic and telephonic communication over very great distances, with an aerial output of 700 watts and wave lengths ranging from 15 to 90 metres. Then there is an emergency transmitter as a special reserve in case of a breakdown in the power plant of the vessel. The operation of the emergency transmitter is entirely independent of this electrical plant. The receiving section consists of a newly designed ultra-sensitive and ultra-selective receiver for wave lengths from 150-2000 metres, with additional tuned band filter. The congestion of all wave lengths use at sea and the need of rapid handling of the wireless traffic demand receivers which by the

greatest possible selectivity and sensitiveness still remain so simple to use that the attention of the operator is occupied as little as possible by the tuning in to a desired station. In addition, the wireless cabin is fitted with a short-wave receiver for wave lengths from 10-150 metres with high-frequency amplification, and an S.O.S. receiver to pick, up at any time an 8.0.5. or alarm signal on wave length 000, independent of all other communications. A special receiver with loud speaker is always tuned in. The ship is fitted with direction finders, which are an indispensable help, to navigation, especially in foggy weather. Four motor-driven lifeboats are fitted with wireless, placed in the covered-in bows of the boats. The necessary current for these small stations (sending wave length 600 metres) is generated by an accumulator-battery of 24 volts and roughly 100 amp. hours. This battery can be recharged, if necessary, from the water-tight enclosed motors. The wave range of the receivers is 3001100 metres. " The two-wire aerial is carried on two collapsible masts on board each boat.