Radio Digest (July 1924-Apr 1925)

February 7 , 1925 RADIO DIGES T— Illustrated Construction of the Six Tube Hetduogen Some Questions and Their Answers By C. E. Brush THERE are several points in connection with hetduogen receiver on which the readers of Radio Digest have requested a little more information. Since some of these points and the answers will prove of interest to those who are building the hetduogen, they are being printed and will straighten out many difficulties Q. — I am about to construct your hetduogen and want a filter, antenna coupler and oscillator constructed along low loss lines and also wish to use litz wire in these units. If you warrant the use of the above construction please give the details in Radio Digest. H. E. S., Pittsburgh, Pa. A. — We have your letter of January 5, and wish to advise that there would be no advantage in constructing the inductance units for hetduogen on low loss principals. Regeneration is introduced into the grid circuits of both detectors so that the effective resistance of both circuits is nearly reduced to zero. The use of litz wire has been stated by leading authorities to be of no advantage below 2,000 meters and, in addition, if one of the little strands^in a piece of litz becomes broken or is not connected by solder the result is far worse than if solid wire were used. Q. — In reference to the hetduogen set that you are publishing, if you are going to heterodyne to about 600 meters will you not get a large number of ship stations through the programs? "Would it be possible to' use a loop on this set? D. L., Windsor, Canada. A. — We have your letter of January 5, and would advise that while we do not know the reason, we found that ship stations and other transmissions around 600 meters are not picked up on the hetduogen. The writer is going to try out this set on a loop, but has not as yet had an opportunity to do this. Tubing Used Q. — Concerning construction of the 6tube hetduogen on page 15 of the January 3 issue — oscillator windings — advise if the tube should be 2% inches inside or outside diameter? R. L. B„ Dalton, Ga. A. — The hard rubber or bakelite tube for the oscillator coupler of the hetduogen should have an outside diameter of 2% inches; the antenna coupler tube should have an outside diameter of 3% inches. These are both standard sizes and the wall has a thickness of 1/16 inch. Q. — I have plenty of number 26 dec. wire and wish to know if I can use it instead of the dsc. How will the volume and tone of the hetduogen compare with the superdyne, that is, tube for tube and ordinarily should I expect coast to coast reception from this city by using the hetduogen? Would I gain anything by winding coils basket weave fashion, and if so, should the same diameter and number of turns be used? T. L. M., Rome, Ga. A. — Number 26 dec. wire will be suitable for winding the coils, providing the proper space is left between the anchoring holes to accomodate it. We would hardly say that you will get reliable or daily coast to coast reception, as we are not familiar with receiving conditions in Georgia, but if any other receiver will do this in your locality the hetduogen will. We doubt whether any gain would be noticed from the use of basket weave coils, as the resistance of the circuits is lowered to the minimum possible by the use of regeneration. Radiation Q. — I wrote your Q and A department some time ago and wish to thank you for the information received. I am now very much interested in hetduogen which is being described in your issues, and wish to ask the following questions. Is the center dial a volume control or is it used to tune in stations? Does the set radiate and bother other receiving sets? Does it whistle when tuning in to a station? T. T. M., What Cheer, Iowa. A. — The center dial on the hetduogen acts as a volume control since it is a control of regeneration in the first tube. This receiver will radiate if improperly handled, as will any other set, since this regeneration control can be brought up too far. If this control is advanced too far, tuning can be done on the whistle of the carrier wave. Correctly operated, however, tuning is done with this control considerably below the oscillation point and this control is then advanced for increased volume. • Hetduogen Best Yet Radio Digest: I am listening to KFI, with WCAP going full blast, no interference. Had KFI, KGO, and KOA last Monday night — loud speaker on hetduogen with five tubes, one transformer and one stage resistance coupled. Am well pleased, but will you please tell me what transformers Mr. Brush uses? Only put up a test set but am starting to rebuild now. I would also like to know what he used that second variable leak for? Won't you please give me the information I ask by return mail. I will buy the Radio Digest just the same as I have a copy reserved each week. The programs alone are well worth the price. I am a locomotive engineer, and have built nearly everything I have found in Radio for last two years, during my spare time. Hetduogen gives promise of being the best yet, or at least the equal of a seven tube super-het. E. R. Riker, 535 North Irving avenue, Scranton, Pa. Q. — Please answer the following questions in regard to the hetduogen. Does tube W use a separate rheostat, and if so, what size rheostat do I need for tubes V, U, and X? If tube W does not use a separate rheostat what size rheostat do I need for tubes V, U, W, and X? I want to use jacks between tubes X, Y, 'and Z; do I need separate rheostats if I use jacks between these tubes? I have three unshielded audio transformers, and wish to know if they will work all right in this set? M. J. G., Howard Lake, Minn. A. — We have your letter of January 2. In hetduogen as built by the writer, tubes U and W are on one rheostat, while tubes V, X, Y, and Z are on another. It would be advisable to have a separate rheostat on tubes X, Y, and Z if you are going to put jacks between them. As built by the writer, there is a jack in the plate circuit of tube Y, and the jack in the plate circuit of tube Z is of the filament control type. Unshielded transformers might work in this set, but if you are going to use them we would advise the installation of but two stages of audio amplification. The use of three stages requires carefully shielded and unusually well designed transformers. Resistance Coupling Q. — The hetduogen as described in the December 27 issue sounds very good, and MACNATRON COMPARISON is a stringent test— but MAGNATRONS have thrived on it. Comparison is the force behind the everincreasing MAGNATRON popularity. Comparison has convinced thousands and thousands of radio fans that MAGNATRONS have no superiors in the field of vacuum tubes. The DC-199, the DC-201A, and the DC-199 with large base, each list for only $4. Your dealer has them! CONNOVEY ELECTRIC LABORATORIES 309 fifth Avenue NEV YORK CITY I am impatiently waiting for next week's Digest. I am anxious to know if I can use resistance coupled amplification, as I have three stages of this type; or must this se have the transformer style of coupling? J. J. S., Boise, Idaho. A. — We wish to advise that resistance coupled amplification can be used in the hetduogen and will probably give equal, if not better, results than the transformer coupled amplification shown. The three stages of resistance coupling will not give quite the volume that three stages of audio will, but there will be no tendency to howl and the output will be remarkably free from distortion. A hetduogen made with such coupling of the amplification should prove very satisfactory. Q. — In checking over the hetduogen subpanel layout and the wiring diagram as shown in figures 10 anO 11, and then looking at the panel from the front as shown in figure 1, I find two rheostats, two jacks and one filament switch. The wiring diagram as shown in figure 2 has only one rheostat, one jack and no filament switch. Please advise whether this is an error or how there is this discrepancy. W. A. F., Greensboro, N. C. A. — The hetduogen hook-up shown in our December 27 issue, figure 2 was not the actual hook-up used. It was intended only for use with the explanation of the circuit given in that article, and all parts such as extra rheostats and C battery, were eliminated so that the essential features might be found as easily as possible. The actual hook-up and directions for wiring are contained in the January 17 issue, in figures 10 and 11, and will be found to agree with the front view as shown in figure 1. Q. — I am not yet a subscriber for your magazine but I buy it regularly at the newsstand and have become very interested in the construction of hetduogen by C. E. Brush. Will you please give me an estimate of the cost of this set when complete, understanding that I buy all materials at regular list price? Will the set when completed be as efficient as the standard make five tube sets on the market? H. D., Kankakee, 111. A. — We wish to advise that the cost of the complete set of parts for the hetduogen at list prices is about $75. Our opinion is this receiver will be just as efficient as any five tube set, and far more selective than most of them. The complete list of parts is in the issue of January 17. Amplifier Tubes Used Q. — Although the construction of hetduogen has been very carefully described in your magazine you have not as yet mentioned what tubes are to be used. I presume that the hard tubes are to be used in all sockets, but will appreciate your letting me know definitely on this. K. L. B., Oklahoma City, Okla. A. — As used by the writer, the amplifier tubes such as "UV-201A or C-301A are used as detectors, oscillator and audio frequency amplifiers. 199 tubes may be used in place of the storage battery tubes, providing of course, that four volts is used at the A battery binding posts, but the volume will naturally not be quite as great as that to be expected from the larger tubes. The writer has not tried the WD tubes, but can see no reason why they would hot work in this "set. Grounding Rotor Plates Connect the movable plates of a condenser to the ground or filament side of the circuit and the effect of body capacity can generally be eliminated. The difference in the connections is more noticeable when weak signals are received. In the case of the antenna series condenser the rotary plates should be connected to the wire leading to the ground, and the stationary plates to the antenna. Graining a Panel To give a special grained finish to a Radio panel, place the panel securely on a table and stroke it lengthwise with fine sandpaper or steel wool. When all traces of the natural polish have been removed, brush the panel with a dry cloth, and finish by wiping with a clean cloth dipped in machine oil. » Operate Sets Construct Paris ImpwveReception UnderstandMio MemhleCircuits The greatest assemblage of facts and hints, from actual everyday practice, ever gotten together. Edited by the technical staff of Radio Digest, it supplies the demand for a book covering every phase of Radio. Starts at the beginning with simple explanation of Radio reception, with technical explanations of the different parts and leads right on to the more advanced instruction. A complete handbook serving as a ready reference in the Radio field. It gives suggestions on parts and sets which will prove to be a money saver. Blue prints and diagrams are essentially an important part of this book. Special chapter is devoted on "How to Operate," which gives detailed information on the operation of many well known sets. A general information is vital to the knowledge of anyone interested in Radio. It gives a complete list of all broadcasting stations with a colored map showing their location. The workshop kinks will save you time and money. Now is the time to take advantage of this exceptional offer. Mail coupon today! RADIO DIGEST, 2-7-25 510 N. Dearborn Street, Chicago, Illinois. Unclosed find $5.00 for one year's subscription lo Radio Digest. The new Radio Book. "Radio Receivers," will me mailed FREE, postage prepaid. Name City State 2-7-25