Questions and answers

Radio Record, Volume V, Issue 7, 28 August 1931, Page 16

Questions and answers

A C. (Milton): I have had trouble * with the first tuned stage of my. three-dial set, in that this particular stage will not tune below 300 metres. I tried removing turns from’ the secondary coil, but by doing this I could not get high enough. The other stages do not give the same trouble, although the secondaries are the same. A.: The trouble is due probably_to the first tuning condenser being smaller than the others. We would suggest your trying the effect of a .0001 fixed condenser in parallel; that is, connected between the moving and the fixed plat of the condenser. PIDER (Shannon): With reference . to the Beverage aerial; should the receiver be ‘at the end farthest from the’ desired station?-Yes. 2. How would it work at the opposite end? A.: It would probably be quite satisfactory. 3. How does the correct Beverage compare with a good: aerial fifty feet high? -A.: It is decidedly superior. T W. (Auckland): I have made up the ¢ "Outspan Five," but it is not as successful as I would like it to be, I yust have the coils wrong, as 2YA is at the top: of the dial and very weak.

What number of turns should be used on the secondary coil? . .: On a Qin. former you. need 80 turns on the three coils, although. the second one might be better if 75 turns only were used. The primariés consist of 80 turns each wound upon Iitin. former and slipped inside the low potential end of the secondary coil. The tickler consist of 80 turns wound on the same former as is the secondary. The wire in the case of the secondaries is 26 and in the case of the primaries 34 d.s.c., and tickler 32 d.s.e. 2. As I am using a .0001 differentia! condenser, would 60 turns on the tickler coil be sufficient? A.: .0001 is a fairly small condenser for this purpose, but with 60 turns it should be satisfactory. 8. What is the screen voltage of a 282 valve? .: On any screen-grid valve, the sereen-grid voltage is approximately half of the plate voltage. XxX R.T. (Arrowtown): I recently in- * creased my battery voltage from 90 volts to 180 and did not receive any greater volume. I use four PM6’s and one PM6D and one PM256. What is the cause of my not getting greater yolume? . .A,: PM6 is a last-stage valve and should not be used elsewhere. Use

PM5X’s in all stages except the detector, where you could use PM6D, and in aan 5 stage, where you could use A. BC. (Timaru): Which short-wave adapter would you recommend for use with an ordinary five-yalve neutrodyne set? A.: One of the type of adapters that tits in to the detector valve. A typical one of these is the "Sparrow Hawk" adapter, which appeared in the 1931 "Radio Guide." 2. Who are the agents of the Rice-Kel-loge dynamic speakers? A.: The National Electric Engineering Company, Jervois Quay, Wellington. Ler (Paeroa): I have a set using a loop antenna. How can IT convert it to an ordinary set? : The easiest manner is to substitute the ‘Toop by an ordinary coil wound on Yin. former, or better still, compare the condenser that tunes the loop with the condenser tuning the first stage. If they are the same, then construct the coil Pe ee ee ee a ee ee

identical with the first coil in your set and place where the loop is now. Tap in the aerial a third of the way from the low potential end, that is the bottom, and connect the bottom with earth. If your set uses regeneration, or is of a superheterodyne tyne. your difficulties are greater. Your best plan in. that case would be to get in touch with a radio engineer and have the job done properly. You appear, however, to have worked out quite a feasible scheme for connecting the set to an aerial. The fact that it brings in a great deal of static shows that it is quite efficient. H IM. (Christchurch): The four-vyolt or AY battery, supplying my two- valve set has given out and I am considering using Daniels cells connected directly to the set. How many cells should I use to operate two 4-volt valves drawing about + amp.? A.: You would require five cells, and you would need to use a rheostat to regular filament voltage. 2: What would be the approximate life in hours with these valvs A.: It is difficult to say. The Daniels eell does not peter out, if you keep renewing the sulphuric acid and the bluestone, as mentioned in the article. J. C. (Dunedin): What acid must be * used for a Balkite charger? Sulphuric acid as obtained from ane service station, added to distilled water, until 1200 "degrees specific gravity is peached, | when tested with a hydro--meter,

W H. (Wanganui): Is there any way * of testing a lightning arrester? A.: Yes, by taking it out of your circuit and, if the set goes better without it, then there is’ something wrong with the arrester, The only thing likely to go wrong in a lightning arrester is shortcircuiting, and this can be detected by aforementioned test. ala 2. Is it detrimental to connect the.earphone ‘terminals to the terminals of an a.e. set to which the loudspeaker is connected ? . A.: It may. be, upon whether or not an output filter is employed between the valves and the speaker terminals, if you put the high voltage that goes to your valves through your phones you are liable to damage them, See the article recently published in the "Radio Record" on connecting phones to a loudspeaker. 8. I understand one does not get the full efficiency from valves after 1000 hours’ use. Is it detrimental to the set if I use them after this time? A.: No, providing your valves are still functioning satisfactorily it is not necessary to change them. Probably, however, you would notice an improvement if you did. . F W.B. (Le Aroha): I have just ou * two new valves in my set, but both of them show a blue light when the current is turned en, The old ones are not like that. ; A.: It appears that the valves are gaseous, and we would advise you to take up the matter with your dealer. Although not harming your set, the valves are not giving the satisfaction they should. 2. Could you tell me the best.type of shortwave adapter to fit to my set? Also the price? . A.: The best type is a super-heterodyne, but we do not know the price of such. They, have been adyertised in the "Record. PARK-COIL (Pukemiro Junction): What does the exciting jelly in a dry battery consist of? , A.: Sal-ammoniae mixed with a depolariser in a suitable paste. 2. Is ammonia in the bottom, and why? A.: It may be used in some batteries, but is not in a standard cell. Y 3. Is the carbon still good,in a dischayged dry battery? . i A.: Yes, it is not affected by the running down of the battery. A M. (Waitomo Caves): If I connect- * ed nine Deniels cells in series would I get 9.9 volts? If so, would this be too high to connect to my accumulator? A.: Yes, it would give you 9.9 volts, and it would not be too high to connect to an accumulator for charging purposes. If, however, you wanted to use the battery direct to your set, you would need to series-parallel the bank so as to break down the voltage and make provision for more current. You would thus get approximately 5. volts. ty YZ (New Plymouth): "What height and length makes a good aerial? A.: For a set such as yotirs, using a large number of valves, we suggest one as high as possible, say, 40 feet, with a ' 50 or 60 feet flat top. 2..What would be the ideal aerial for selectivity ?

DX N otepaper DX’ers! Write for that verifieation on D.X. notepaper and avoid missing out important details. Takes a quarter of the time to write out, too. Obtainable from P.O. Box 1032, Wellington, in two-dozen lots (minimum order), price 1/6, or six dozen for 4/-, post free. Special paper for club members. .

' _A.: 100 feet would tend to make the ._SPt quite selective, but by reducing it u would get a still greater separation between the stations. As far as signal strength is concerned, you can have almost any length, up to several hundred feet. Generally speaking, however, a 100-foot aerial, such as we have described, would be the best for all-round ‘results. L TJ. (New Plymouth): I have suc- * cessfully constructed the 2 rf. parallel feed Browning Drake circuit with & moving coil dynamic speaker. At first I was not successful with the latter, as there was too much rattle, so I -altered the design, making the moving coil and the cone into a fixed unit, thus simplifying matters, and making the cone more responsive to the vibrations of the voice . coil, I was also able to make the gap, in which the voice coil moves, half the size of that specified. This speaker gives more than double the volume of the ordinary magnetic: speaker, using about 10 watts in the field. I have also been experimenting with a erystal circuit, and have been ag ic receive the local station, 2YB, and alSv1YA, 2YA, 2BL, 2FC, 4QG at night, and also to hear faintly music from other stations. I have not heard of anyone being able to do this. (Neither have we.Tec. Hd.). I have a good aerial and earth 70 feet high and 140 feet long. What is the best arrangement ‘of Philips valves to use with my Browning Drake set? rir A609, A409, B415, and B409, 2. Would sereen-grid valves be satisfactory? A.: Yes; you could alter your set to the design of the Outspan Five, and no doubt you would get better results than you are now getting. J OH (Greymouth): How many times more powerful would the Outspan ‘ive be than an old model five-valve neutrodyne using 90 volts "B" for the plate? , A.: It is rather difficult to make a sgomparison in this manner. All we can "eel you is that the Outspan Five would e definitely superior. 2. It is my intention to build the Outspan, but am a little at sea regarding some of the distances you mention. If I forwarded you a suitable drawing would you mark them in for me? A.: Yes; send along your drawing and we will see what we can do for you. 3. Do two power valves in push-pull give double the volume that one does? A.: No; they give a greater undistorted power output than one valve. Amplification will be the same as a single valve. (IX234 (Cambridge): My aerial is 60 feet high and 100 feet long, the top giving about 160 feet in all, including the lead-in, which is heavily soldered on to the top portion of the aerial.- The set is not selective at ‘present, and I am of the opinion that if the length of the aerial were reduced say 100 feet the selectivity would improve, but would distance-getting reception be interfered with to any extent? y.A.: We are afraid it would. Whenever 4 Bet is made more selective its sensitivity is decreased. You must have one or the other, or a compromise between them both. Certainly not the two at once, C C. (Christchurch): We cannot tell * you accurately what the voltage -Wwill be at the point indicated because you have not given us any details about your choke. It will depend upon the number

of ohms resistance in that piece of apparatus.’ The drop in the valve is almost negligible, something in the region of 10 volts, An average choke would drop about 40 volts, so that you would have roughly 700 volts. . A W.M. (Dunedin): I am constructing * the "Outspan Five" and am at sea as to the coils, for I have on hand -0005 condensers. Could you supply me with full information for the number of turns, using .0001 reaction condenser? A.: The secondaries should have ‘72 turns of No. 26 d.c.c. wire. The primaries each about 25-30 turns, and the tickler

coil 40, but this ean be very much finer wire. It can be even No. 38 and still retain efficiency. 2. Is it absolutely necessary for the coils to be shielded?-yYes. 8. What is a vacuum tube voltmeter? A.: A vacuum tube voltmeter is a sensitive instrument employing the circuit of an ordinary anode bend rectifying valve and a very ‘sensitive meter or galvanometer. We reproduce a diagram of a vacuum tube voltmeter herewith. It is operated by varying the grid bias until no direct current flows. The incoming r.f. current is rectified and flows as a.f. current to the plate circuit of the valve. This direct current operates the direct current galvanometer. If we allowed the ordinary d.c. current to flow in the circuit the meter would be destroyed. Such a meter can be used for measuring the strength of signals from gramophone pick-ups, crystal sets, ete. All laboratories use them. (TUBE (Invercargill) : I intend to erect a higher aerial. Will I pick un more static and atmosnherie noises with an aerial that height, than with one 40 or 50 feet? A.: Generally the higher the aerial the more are the atmospheric noises that one picks up, because they decrease toward the ground. However,. you would get greater signal strength. Keep the top quite short and depend upon the lead-in for length. This will give you the best results. ; 2. My local dealer insists that a good earth is out of the question_unless it is making contact with clay. You say that "unfortunately, clay, especially wet clay. is not the best of earths because it offers So much resistance." Whom am I to heglieve? A.: Sorry. O.M. we cannot enter into controversies of this nature. We have made a statement which we believe to be correct, and we have based our assump-

tion upon measurements taken by the Bureau of Standards in America. 8. Which is the next best earth to the Pierce earth system? What about a copper sheet 2ft. 6in. long, 18in. wide, with the earth wire soldered to it at three different points? A.: We, think this would be an excellent earth; although listeners claim to have had great results with the Pierce earth . system, still we are sceptical. Measurements tend to show that no improvement can be had by arranging an earth system such as Pierce has done. STATIC (Christchurch): I have been able to log only one American station, though I have a fairly good aerial. What is the trouble? A.: Why some people cannot receive American stations and others only a small distance away can receive them well, is something of a puzzle. Your aerial could be improved, but still it is not bad, and many people are receiving the American stations on a very much inferior outfit. Look through this month’s "Radio Log" and you will find out what type of installation the people who won the competition are using. Locality has a tremendous effect upon very long distance reception. Fuss (Christchurch) : On tuning to a station the set chokes and music gurgles through very weakly. Moving the dial a few degrees the set roars and motorboats. What is the matter? A.: It sounds as though you are overloading your set. Very few sets can be turned in full blast to a strong station. If, however, this happens on weak stations, the indications are that your set is oscillating when the condensers resonate. This can be due to a defective bypass condenser, or to the absence of such a condenser. Try a 2 mfd. condenser between B-- r.f. and earth, 2. Why shvuld the set not go on the first jack and yet on the second jack? A.: It sounds as though the jack is not connected pronerly, doesn’t it? W H.D. (Wellington): Can you sug- * gest a suitable set of valves for an American five-valve battery set? A.: You do not state what model set you are using, and as the valves are different for each model we cannot help you very much. ; a : 2. Reception from outside stations is very poor. Is this.the fault of the valves being in the wrong position? A.: It is unlikely the valves will be in the wrong position, but it is: quite possibly due to weak or defective valves. Your best plan would be to take them in to a dealer and have them tested, _ ask him what ones should replace them. K M.D. (Wellington): Would it be * possible to alter my set to take a %.g. valve in the hf. stage? A.: Aceording to your circuit it will be quite a simple matter, but, after all. the circuit is not the only thing that counts in changing a set over from triode to sg. rf. You see, so much depends upon the layout of the set; you may be hampered with the shielding or the wiring may not be easily accessible, Furthermore, can you get adequate interstage shielding on it without seriously

modifying the layout of your set? All. these things must be taken into consideration in changing a set over from triode to sg. Usually it is not a practicable proposition. PURUEI (Marlborough): Pleased to hear of your results and are glad to hear from you. We always like to hear from correspondents after they have remedied the trouble that was worrying them. DX JUAN (Napier): Could you let me have the circuit and full details of an all-wave a.c, set? A.: Yes, the Advance A.C, Short-wave Set described in the "Radio Guide" is the ideal one for your purpose. You can get a "Guide" if you are lucky for 2/6. Your present’ set is certainly out of date, and you would notice a big difference if you built the "Advance," Your method of connecting the choke and resistance volume control could, we think, be improved upon. The optimum aerial coupling is a third of the way from the earth end. Now, if you turn the slider down there you will have very little resistance between the aerial and the earth, and consequently would lose all you gain from it being coupled there. If the resistance is ‘variable, without the variation having any effect upon the aerial coupling. it will then be quite satisfactory. We think if you carry out these changes the rather peculiar phenomenon you speak of will disappear. We can understand the set working without an earth, but if you can put the earth on to an aerial terminal and put the aerial on as well, and still get signals, (Concluded on page 30.)

(CORRESPONDENTS must attach this coupon to all queries sent to the Technical Dditor (Box 1032, Wellington. Limit three questions, unless letter is accompanied by 1/ee. Name of set otc nccccecccccce Number of valves Seeeeceesessecsess Name Address Coro e ren esecesccsenesensecccecccces’ -Nom ‘de plume ovecnccccccaveccces To be kept in subsequent inquiries, . Date .....2....... Please Note:see ere eee (1) Be specifie and brief, tabu- -- e lating, if (2) Write legibly, and on one side of the paper. (3) We do not design circuits, but accept suggestions for feature articles. Solving trouble, as different from advice, is difficult by correspondence and while letters are given every consideration, answers are not necessarily correct-they are only our opinion based on the matter supplied, which may be quite inadequate, Intricate and involved specifications cannot be ‘supplied without a specialist’s fee, Ol Oa i). jaan). () SD) ee (> 40a 0 ae

Questions and Answers (Continued from page 18) the indications are that there js something. wrong with your earth. pownR VALVE (Dunedin): I cannot get the specifications for short~ wave coils for my kit set. A.: Write to the N.Z. agents, Box 462, Auckland, 2. Would a-secreen grid valve make very much difference to my set? A.: 1¢ would improve it, but it would be awkward. to adjust your present set to take an s.g. valve. F J.S.. (Te Aroha): I have a battery set ~ * and am using a 3002 type eliminator.. Could you tell me the best types of valves to use? _ A.t We suggest the 221 valves in #ll stages except the last, where you should use a B605 type. You could pee Ms in the last stage. instead of