Radio broadcast .. (1922-30)

How to Use a C Battery — A B-Substitute with Resistance Amplifiers —Modifications in the Audio Output — Details of Home-Made Coils By HOWARD E. RHODES "N THE November issue of RADIO BROADCAST there appeared the first of several articles describing the RADIO BROADCAST "Aristocrat", a five-tube receiver designed to give excellent quality of reception, combined with selectivity and sensitivity. It consisted of a stage of tuned radio frequency, regenerative detector, and a resistance-coupled audio amplifier. It appealed greatly to home constructors because of simplicity of construction and its exceptional tonal fidelity. The circuit is a remarkably efficient one and meets the requirements of the DX fan in a highly satisfactory fashion. Some of the models used a Hanscom single-control tuning unit so that the utmost simplicity of operation was had, while other models used dual control, preferred by many people. The "Aristocrat" has proved extremely popular and there have been many requests for further information concerning batteries, tubes, home-made coils, B substitutes for use with the set, the best method of assembly, etc. In this article we are going to discuss some of these interesting questions. Constructional data appeared in the November, 1925, RADIO BROADCAST and will not be repeated here. In the first place, there is something to be said about assembly. Whether or not a sub-panel is used depends upon personal preference. The set will, of course, give satisfactory operation with any good electrical assembly. The various methods of construction can readily be seen by reference to the accompanying photographs and those in the November, December, and April issues. The sub-panel layout illustrated in Fig. 4 uses a Bruno Bracket and makes a very neat job. The base board assembly will appeal to others and it is well illustrated in the photographs in the issues mentioned above. The "Aristocrat" is an exceedingly simple circuit to put together — not at all tricky — and any standard procedure can be successfully followed. MAKING YOUR OWN COILS THERE are a great many radio home constructors who like to build their own coils and Table i presents complete data for the construction of various types of coils which can be used in this circuit. There are also a large number of manufactured coils that can successfully be used in the "Aristocrat" hook-up. Excellent manufactured coils are made by the following companies; Hammarlund, Eastern Coil Corporation, American Mechanical Labs Inc. (Clarotuner), F. W. Sickles Company, Perfection Radio Mfg. Company (Supercoils), Victoreen Radio Products, and several others. There have also been some questions concerning batteries to be used with the circuit. Particularly with regard to the C battery, there seems to be some confusion as to just what factors determine its value. The bias voltage should be determined by the strength of the signal that is to be handled. A uv-2oiA should not have much more than 45 volts of C battery when used in the output stage with 135 volts on the plate. Increasing the grid voltage beyond negative 45 volts will result in decreased power in the plate circuit. Actually, the power in the output circuit of a uv-2oi A is not sufficient properly to operate a loud speaker and it is always best to use a semi-power tube in the last stage. These tubes will be able to handle a stronger signal and this change will also result in better operation of the speaker at a power level more nearly correct. Table 2 gives the correct value of C battery to use on each stage of a resistance-coupled amplifier when 135 volts is used on the plates of all the tubes. Practically, not much difference will be noticed if the first two tubes are operated at a lower C voltage, since the lower voltage need not necessarily result in distortion if the signals being handled are not very great, but will only produce a slight decrease in amplification, not detectable by the ear. The important point that should come out through this discussion is: Don't make your C battery voltage much greater than is necessary Regeneration may be Obtained Either by Variable (Tickler or Resistance Shunted AcrossAFixed Tickler ^Inside Terminals of Secondaries^ !> 500.50,000-n Circuit Enclosed Herein Comprises Resistance Coupled f Amplifier which may be Obtained as a Complete Unit Separate Retrstor Units may be Employed in the Audio Amplifier^ r where the Complete Manufactured Amplifier is not used 1 FIG. I The circuit diagram of the "Aristocrat" incorporating the modifications mentioned in this article. Note how the C battery is connected and also the_addition of a choke and condenser at the output, so as to keep the battery current out of the loud speaker windings. This diagram will be useful for those wishing to use a C battery on all the amplifiers