Radio broadcast .. (1922-30)

Revamping the Silver Super-Heterodyne 503 signals. This control is not critical except that if too high a value of condenser is used the first detector tube will oscillate and become unstable. The condenser may be located above and between the two tuning condensers on the portable model also, if it is desired to take advantage of the full amplification possibilities of the set by means of this one additional, but fairly non-critical adjustment. Binding posts may be located on small bakelite strips on the sub-base so that they will not appear on the panel. This will add somewhat to the appearance of the set if it is to be used in a permanent installation. WIDE LATITUDE IN ASSEMBLY T^HE assembly can be changed to meet * any individual conditions of height, depth, or length, such as might be imposed by a phonograph cabinet. The amplifier assembly should not be changed, but the oscillator coupler and first two tubes may be moved up against the panel between the two condensers, which will have to be located farther apart. The entire amplifier section may then be shifted behind this portion of the set, which will make an assembly 12 to 15 inches long and 8 to 10 inches deep. (See Figs. 6, 7, and 8 of the article on the portable receiver.) It is also possible to locate the amplifier section above the condensers and first two tubes. The size would then be approximately 10 to n inches high, 12 to 15 inches long, and 6 to 7 inches deep. These variations are only suggested where the constructor wishes to meet particular space requirements, and feels confident that he will be able to work out the changes satisfactorily. TESTING AND TROUBLE SHOOTING Filter Condenser: The value of the condenser across the RF unit terminals 7 and 8 will vary between .0075 and .01. It is best to start with .0075 and then build up to .01 by adding .0005 and .001 condensers in parallel with the .0075 condenser. The best value will be where the oscillator dial reading is sharpest on a comparatively strong local signal. The proper number of condensers may be bolted together with machine screws and nuts and soldered in position on the wiring. Grid Leaks: For 201 -A tubes the grid leaks should be from ^ to 2 megohms for the second detector. One megohm is satisfactory. A grid leak from 2 to 5 megohms should be used for the first detector. The higher value is preferable. Grid leak values for 199 tubes are given in the October, 1924, article and the same values are correct for ov-3's. For WD-I I's or wo-12's they will be approximately the same as for 2Oi-A's. Filament Returns: In the portable receiver, the first detector grid return, or center tap of the loop is shown going back to the negative side of the filament, and for the second detector, terminal 9 of the can leads to the plus side 2 RAN6E VOLTMETER WITH FILAMENT a PLATE VOLTASE VOLTMETER RESISTOR I RANGE VOLT ME TEH TOR DETECTOR OB AMPLIFIER PLATE VOLTA6E VOLTMCTER RCSIST4* FIG. 6 Wiring details of voltmeter which can be used with advantage in the super-heterodyne of the filament. In the laboratory model both these returns are shown to the negative side of the filament. It is not of very great importance which connections are followed out, although it would be advisable to keep all returns, including those of by-pass condensers, on the negative side of the filament line. Overloading: Due to the extreme amplification, about 55 per stage (voltage) with 201A or ov-2 tubes, developed in the intermediate amplifier it is sometimes possible to overload the set on strong local signals. This may be overcome by some of the suggestions offered in regard to the portable super-heterodyne or by connecting grid leaks of j\ to j megohms across the radio-frequency amplifier tubes from grid to plus or minus filament. Potentiometer Control: In the case of 2OI-A, ov-2, uv-i99, or ov-3 tubes, the potentiometer control will probably be satisfactory in that the volume of stations may be reduced by retarding its arm toward the positive side. If this is not possible, decreasing the value of C battery on the RF tubes will remedy matters. On WD-II'S or wo-12's, good control will be difficult to obtain and the C battery will have to be set at the lowest value commensurate with good