The Berlin Radio Exhibition

Radio Record, Volume III, Issue 25, 3 January 1930, Page 8

The Berlin Radio Exhibition

: Differed from English and ‘American ~

HIS exhibition, comprising the products of over 300 manufacturers, could be divided into three sections dealing with transmission, reception, and the work of the German Post Office in encouraging research. _ The transmitting section included the whole of the apparatus used by the Witzleben station and the wonderful broadcasting tower, 420ft. high, with a splendid restaurant 170ft. from the ground and a cafe at the top. Compactness of Receivers. HE) most striking point was. the amazing compactness of receiver design and the ingenuity of designers in packing away components in the smallest. possible cabinets. Every maker of repute had at least one cheap three-valve set selling at £2 or less, complete with valves. These sets were all constructed in Trolite mouldings about 8in. square, with the valves and plug-in coils mounted on the top, and most of them had resistancecapacity couplings in a simple detector and two stages of audio. Selectivity is evidently a very important characteristic of a set for Central Huropean use, and even the simplest and cheapest sets had a loosecoupled aerial circuit. Portable sets are still almost unknown in Germany, and the three or four exhibited attracted considerable attention. Most were three-valve localstation receivers, but one, the Lorenz, was a six-valve super-het, and picked up 2L0O at excellent strength in daylight. Many Self-Contained Sets. THE self-contained receiver, as distinct from the portable, was represented in all the leading makes, and eould be obtained in every case to work with the mains. Whereas most ‘English sets of this type are primarily receivers,. with the addition of a loudspeaker, all :those on show were primarily speakers, with the set hidden away at the back, and in some cases the only external difference between a complete receiver and a, simple loudspeaker was the addition of one small knob. A year ago all-mains sets were practically unknown on the Continent, but now there is an enormous variety from No to choose, both for A.C. and These sets are built on a metal chassis and enclosed in a metal cabinet which has a switch and fuse incorporated in the lid. ae Prices range from £4/10/- for a twovalve set to £27 for a six-valve superheterodyne, all including valves. Many sets use a screen grid valve, and some can be adapted for short-wave work. Short waves are coming into favour very rapidly on the Continent,; and among the stands of the component manufacturers there were many ingenious tuners which could be used on either short wave-lengths. or on the ordinary broadcast. band. .

Four-volt Valves Universal. IN the valve exhibits there were not nearly so many types available as we have in this country and all valves designed for battery operation had 4volt filaments, as the 2-volt and 6-volt ranges are now quite extinct in Germany. The only exception is the Telefunken RV218 and a valve of the LS5 type which works on 7.5 volts. Screen-grid valves were well represented, a good example having an amplification factor of 500 and an impedance of -700,000.ohms. Pentodes included the three types, the best having an amplification factor of 60, at 300 volts on the anode, the impedance being 33,000 ohms. H.C, valves were of both types, the indirectly-heated cathode valves taking 1 ampere at 4 volts and the direct-ly-heated variety taking from .25 to 1 ampere at 1 volt. Screen-grid valves were included in both groups, and there were also special double-grid generalpurpose valves designed to function on low anode potentials, of the order of 20 volts. Coming to loud-speakers, the movingcoil instrument had gained an enormous popularity during the past year. Nearly a hundred types weré on exhibition and every manufacturer had a demonstration room attached to his stand so that one could compare the different kinds. Lack of Brilliance. ON the whole, the quality of reproduction was very good, although somewhat lacking in brilliance according to English standards. Prices ranged from 30/- for movements alone to £20 for large cabinet instruments. ; The popularity of this type of ‘speaker has made it necessary for owners of small sets to add power amplifiers, and many of these were on show, mostly mains driven and of the unenclosed chassis type. Push-pull circuits were not common, but most of the amplifiers had parallel output valves. Rectification of the anode supply was carried out by glow discharge valves, metaloxide rectifiers with one or two exceptions being used only for the field coils of moving-coil speakers. ~ No horn speaxers were exhibited, with the exception of one or two very cheap ones, but there were large numbers of the cabinet cone type, mostly costing about £2. Very large speakers of this typé, capable of giving enormous volume, were available, and these were all driven by heavy four-pole movements. A Complete Range. AMON GST individual exhibits, that of Grawox was one of the most comprehensive, including every type of speaker from small cabinet models to large public-address instruments. Every loud-speaker manufacturer also had a gramophone pick-up on view, and it is no exaggeration to say that there was not a single valve set in the exhibition which was not fitted with terminals or sockets for gramophone work.