Radio Broadcast (Nov. 1925-Apr 1926)

JANUARY, 1926 RADIO BROADCASTS UNIVERSAL RECEIVER 335 In this end view the use of other brackets is Ehown. The builder may use either type according to his own desires ceiver is 32 inches); 2 Detector coil supports, as illustrated in Fig. 2A; 1 Antenna coil support, as shown in Fig. 2B; 1 Neutralizing condenser support, as shown in Fig. 2C; 1 Royalty, 500 to 50,000-ohm variable resistor; 1 each Electrad, .00025.002 and .0005-mfd. fixed condensers, and the following General Radio parts: 2 coils, type 277D; 2 variable condensers with vernier attachment, .00035 mid. capacity, either S.L.W. or S.L.C., type 247P; 2 Dials type 310; 1 neutralizing condenser, type 368; 2 audio-frequency transformers, 2:1 ratio, type 285 L; 4 sockets, type 156 for use with tubes having uv base, or type 349 ux sockets for tubes with ux bases, as explained further along; 1 binding post strip, with 8 posts, type 138Z; 2 rheostats, 10 ohms, type 301; 1 Yaxley filament switch and phone jack and one Electrad grid leak resistor, 2 megohm; and the large \ to 1 mfd. condenser across the B batteries is optional, but advisable. One each \ and \ ampere Brach or Amperite filament ballasts and mountings. BEFORE BUILDING THE RECEIVER TPO BEGIN with, the combination which * we have found to meet nearly every occasion, except where the storage battery is impossible for one reason or another, is the circuit in which 201 -a type tubes are used in all sockets except the output of the amplifier and here we have found the ux-112 very satisfactory, when operated with 135 volts on the plate and a negative bias of approximately minus 9, as shown in the diagram, Fig. 1 With this arrangement, using the proper plate and biasing voltage (B and C) on the radio frequency tube as indicated in the same diagram the plate current consumption is in the neighborhood of five milliamperes and should not be above seven. The ux-112 will increase this figure somewhat. This sum is very low for a receiver of this general type and is one of the outstanding features of the Radio Broadcast Universal. If your receiver is to be located more than fifty miles from a broadcasting station, you may find that one low and one high ratio transformer will give you more volume and in such cases it is advisable to use it. It should not be more than 6:1, however. If this combination of transformers is to be used, be sure the high ratio transformer is used last and not first as is common practise. The reason for this change is well covered by Mr. Keith Henney, Director of Radio Broadcast's Laboratory, in his article, Tubes: Their Uses and Abuses, in our last number. The matter of sockets is a rather important one, in view of the great number of tubes already on the market and those which will probably follow. We have found that the standard socket is just about as satisfactory at the present time as any, because the standard tubes will fit in them and so will the tubes with the new ux bases. Where either the wd-ii or the uv-199 types of tube are to be used, they may be placed in the standard sockets by means of adapters. So much, for the receiver when the tubes to be used are those with which we have become quite familiar. Now for the dry cell operation. We have found the combination of three 199 and one 120 tubes, or their equivalent, to be very satisfactory and, if you contemplate the building of this receiver without using any of your present stock, we suggest that you use the new type of socket because it may be used with any of the new tubes and it will be remembered that both these tubes are soon to be on the general market with the new ux bases, and by using the ux sockets, it will be possible to convert your receiver from dry battery operation to one which may be used with a storage battery by going to no greater bother than changing the tubes. Many of the independent tubes have been found to be very satisfactory and most of them will be on the market within a short time, probably before this article gets into circulation, with the new type bases. In order that you may have a direct comparison of the two types, we illustrate in Figs. 6 and 7, just how they will look when completed. The proper use of any type of tube in any receiver is one of the greatest factors in determining its performance and we can not urge too strongly the careful reading and then putting into application the instruction sheets which accompany the tubes now on the market. BUILDING THE RECEIVER AFTER procuring all the necessary parts and properly bending and drilling all the brass fittings and the wood subbase, the drilling of the panel can be undertaken and the layout shown in Fig. 5 will be found helpful in this connection. Next, all the parts which are to be directly attached to the panel should be put in place as should those which are to be attached to the sub-base. From this point on, the work of assembly is a very simple matter and it is but necessary to fasten the sub-base and the panel together by means of the brass supports and attach the binding post strip, which acts as the rear support for the receiver and then go ahead with the wiring. The dimensions of the entire assembly are such that the completed receiver will fit into a standard 7 x 18-inch cabinet and the use of a cable lead to the batteries is handy and is FIG. 15 So much equipment in such small space is, in itself, an accomplishment. This layout of the Samson TC Receiver is a little difficult to approximate but when you have it finished it's a real receiver. The tests run on it in our laboratory revealed it as one of the best receivers we have ever used. It is compact, easy to handle, economical to use and the tone quality is far above the average. On the second stage audio it performs very well with a cone speaker which is saying much for a transformer-coupled audio receiver FIG. 14 This view of the rear of the Universal gives a pretty good idea of the disposition of the various parts. In this particular receiver, larger tuning condensers have replaced the .00035 mfd. variables. However, for the broadcast range the .00035's are entirely satisfactory