Questions and Answers

Radio Record, Volume V, Issue 51, 1 July 1932, Page 15

Questions and Answers

" AMPSRITE" | (Taranaki): I have made up 2 simple shortwave set and it wil) not oseillate. I have tried all the usual cures, but can only make it work properly by placing my hand on the rf. choke. A.: Try another z.f, choke. Althoug you are using a good one, this is at fault. If you can get your set ta oscillate only by putting your hand on it on certain bands, it dooks very much as though this is the cause of the trouble. Break the connection between the primary and the secondary. failing _ this, bring in the aerial throngh a fixed condenser of about .0001 to the top of the grid coil. Take the lead from the eholre to the fixed plate of the reaction conSennen instead of from the plate of the valve. D804 (Invercargill) : Gan I use two in push-pull, as per my diagra. A™ Theoretically your scheme will he quite practicable. It is questionable, however, if you would get good results, 2. Using 18 volts bias, about what would be the drain from 105 volts h,t.? A.: We do not have a curve of this yalve ayailable, but believe it to he about 2 mamps. for both valves, 3. How does one calculate the impedance of a speaker for matching purposes? Would the d.c. resistance be of any use for calculating ratio of output? A.: We are afraid there is no prac: tical way for calculating impedance. It ig neeessary to measure it, and to a devee it ig quite independent of d.c¢, resis- _ tance. Impedance is built up on this factor and reactance, being the product of inductance, frequency, self capacity and a fixed quantity. If you are using a magnetic cone speaker you could use a rie transformer, and you would not be ‘ar out. "BENG" (Hamilton BH.) : I intend to add more cella to my Hdison B battery. What is the strength of the potassium hydroxide solution, and -how much lithium hydroxide is added? A,: The electrolyte consists of 21 per cent. solution of potassium hydroxide. Lithium hydroxide is added in the praportion of 50 grams per litre. Do nat attempt to make these solutions up your: gelfemany chemist will de it for you for next to nothing, 2. I am enclosing a sample of the substance I use for spreaders. What is the material, and where could I procure t A.: It appears to be a composition bakelite, Your best plan would be to send

ui a sample to 3 well-known dealer and ask him if he can procure it for you, and at what cost, C G.M. (Wellington): Could you give * me the constants of the shortwave adaptor shown herewith? ; A.: Particulars of the could be found from any standard list. For instanec, if your are using two .00035 condensers, one at Cl and the other at C2, the coll particulars would be as folOw t-

Wind the primary with 80 dsc, The other components will be as follow:--RI, 25,000 ohms; 8, .225---.5meds. ; TA ordinary shortwave rf. choke; (C4 an .0001--.001 mfd. condensers, 2. What is the "J" feature referred to in the adaptor? A.: We do not know; it is a reference evidently to a commercial device. "Mus" (Wanganui)..-I am desirous ’ of eliminating a.c. hum from the power transformer. Would shield and earthing same eure this? A.: First make certain that all the laminations are tight. Slacken off the nuts holding them together, and if necessary pack with extra stalloy. Drive a wooden wedge in between the core and the winding, only make certain that in_doing this you do not injure the latter. Shielding and earthing a transformer would cer tainly make it quieter. Ak (Waitetung).-What are the correct types of valves used in the "Rar diogram Five"? A.: A screen grid valve, a special detector, a g.p, audio and aq high gain power valve, 2, What is the correct B voltage for the same set A.: You want from 90 to 120 volta, preferably the latter, with a grid bias according to the valve used in the last stage. This will probably be in the region of 12-15 volts. 8. Can the coils for the "Radio Gra Five" be purchaged ready made? A.: Yes, any dealer will make them up for you. ’ " pOEe" (Hekianga).-Would the wire sample enclosed, be, suitable for a lead-in direct from my aerial ; A.: Yes, it would make a good but there is little point in insulating it so heavily, If you have some on hand use it. If you intend to buy it, use enamelled, it is much cheaper. COovered wire prevents corrosion of the aerial. B S.D. \Wanganni}: Would it weaken -"° a power transformer to join the winding?--No, provided the joint is carefully soldered and insulated. &, I have a idin. x 1din. stalloy core, the sizes being 4fin. x 2 &-8in. Would | the number of turns for this core be the ' same as for the 150 watts size in the | "Guide®? | Aas Yes, 3, In the "Guide" you say to precede a pentode by a frst audio stage is generally looked upon as 2 scheme for inviting instability. Does this statement also apply to preceding vush-pull pentodes by a first audio? A.; No; in this case you have 4 much greater available grid-swing and consequently can use pre-audio stages, ¢.g., the watts amplifier described in the 1932 "Radio Guide." D-Deiwv (Ohakune Junction): When *" tuning from 1500 ke. with the volume contro] fully open the set breaks into oscillation, and increases in inten-

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sity until the end of the dial is reached. The local agents have been unable to remedy: the fault. . A.: There is undoubtedly a fault in your set which only a systematic search with suitable test instruments could reveal. However, it could be suppressed by inserting a 500-1000 ohms resistance in series with the grid of one of the r.f. valves. This resistance could very easily be put in without pulling your receiver about in any way. ‘The dissipating qualities of the resistance need be very small indeed, as it is not called upon to pass any current. Maybe there is a shortcircuit in one of the chokes, and this would not be easily detected. It may help you to bring the serial in successively to the grids of the three screen-grid valves and to make the test for oscillation. It would then be possible to discover in which stage the trouble lay. We are picking it to be the second valve, possibly because L4 has short-circuited. If the trouble has always been the same it may be necessary to further de-couple the stages, but this is quite beyond the capabilities of the average amateur. "AUPER SIX" (New Plymouth): I have built the ‘Super Six,’ but the stations can be received on two places on the oscillator, and the set will not get 2FC at night on the loop. A.: It is quite in order for the oscillator to bring in the stations in two positions, One at the sum of the frequencies, two, at their difference. Your locality is possibly against 2FC being brought in at night. We are sorry your previous queries were mislaid. L S. (Sydenham): Would ice made from tap water, when melted in an earthenware vessel, be suitable for use in an Edison B battery and in jars of B chargers? A.: It wouldn’t be safe to do so, It would be better to collect rain water in the earthenware vessels and use that. H E.L. (Miramar): I intend to con- * struct a transformer for an eliminator, but am not clear 4s to how to calculate the number of turns for the filament voltage on different-sized cores. I could not find any table in your "Radio Guide." A.: A suitable table appears on page 146, giving the number of turns per volt as 9. It is not easy to calculate’ the number of turns per volt. However, the figures given will bé near enough for most practical purposes, _- OCO." (Wanganui E.): I have an umbrella aerial of approximately 100-130 feet in length on 65 fect masts. "My reception of short-wave stations is only fair. Can I improve my shori-wave reception by making any, alteration to the aerial? A.: Yes; it is far too long. Erect a much shorter aerial for short-wave, and do not exceed 100 feet, including the lead-in. You are using about 165 feet in all. Try first of all reducing the effective capacity of the aerial by the usual -OUU1 condenser in series, What type of aerial is best for the operation of an all-wave set? A.: An aerial of no greater length than 100 feet, while a single wire of from 30- _ 40 feet would be more effective for shortwave reception. A W.L, (Petone): What are the re- * quirements of the radio serviceman’s examination? Is Morse included? . A.: A syllabus of the examination can be obtained from the registrar. It entails only a knowledge of simple service proeedure, together with the basic principles underlying radio. Morse is unnecessary. N B.X. (Auckland) : Would a C battery * improve my set when used on the broadcast band, and not spoil the shortwave reception? A.: We are sending your diagram markre showing where to include the C batery. "GATANAS" (Auckland): Reception from 1ZQ and 1ZS appears to be harsh compared with other stations. If

the dial is moved slightly off these reception is distorted. The same to a lesser degree applies to 1ZR. | A.:‘In modern superheterodyne circuits the slightest variation’ of the tuning: dial from the exact resonant point, that is, the loudest point.on the tuning dial,. causes distortion. However, it should be quite clear from the two local "B" stations, providing they are tuned in accurately. Turn the yolume control down very low, and tune for maximum signal with the centre dial, and then adjust the volume. If it is still harsh and not so, on’ other stations, the trouble is probably in the. stations themselves, but if the same symptoms are noticed over a wide number. of stations, the trouble then can be blamed to the set. 2. Should the set oscillate? If so, at what point? ‘ A.: N .: No. "Tt '3. Would bad weather conditions result in the trouble explained above? It is’ most unlikely, A FF. (Pahiatua): How can I tune in * to American stations? I am using a five-valve set. with three 45 volt: blocks. A.: The ability to pick up the Americans depends very much upon your local-ity-and on the’ condition of. your. aerial and earth. Your set is not a particidarly powerful one, and. you may have: Ait culty in logging them.. . W K. (Christchurch) : What is-the ef- * fect of insulators in the stays supporting the serial mast? ae A.: The use of insulators prevent leakage, mainly through capacity effects, from the aerial to the stay wires and where a steel mast is used it is preferable to have them, but not absolutely essential. After all, they do not make a very great difference. "TYBIQUE" (Wellington): I have a shortwave converter attached to my superheterodyne set. I do not. require to use the 65-200 metres on the shortwave and would like to use two valves for the shortwave converter on the. broadcast band, and still retain the 20-65 metres band. Js this practicable? : A.: No; the valves in a shortwave adapter rarely amplify. Their function. | ‘s merely to transform the high frequency impulses picked up by shortwave to frequencies that can be amplified by your broadcast set. If the frequencies’ already can be amplified by the- set, the double version would serve no useful purpose. Certainly it would not amplify. 2. The volume on the 25-60 metre band. is poor, whereas the broadcast set is good. Would it improve matters if I connected the aerial lead from the converter to some point other than the aerial terminal of the broadeast set? A.: The aerial should be connected to the aerial terminal on the converter and the output terminal of the converter to the aerial of the set. JUlave you it connected in this way? We would advise you to get in touch with the dealer who sold you the converter, The yolume should be quite good on the 20-65 metre band. G> (Nelson): My battery set. has developed a persistent crackling, whiyh sounds like weak static. It disappears completely when I push the jack plug into the four-valye point. . A.y There is'a ‘bad coniiection in the last stage of your set.. -Is the volume all that it used to be? Possibly the primary of ‘the-inter-valve transformer has broken down. | Look over, the last stage ‘for loose tug at the wires to make certain that all joints are sound. Go over the fifth valve jack, clean it from dust, and make certain that the contacts are good. ‘Trace the wires from, the speaker terminals to .their ‘destinations and see if they are good also. A B.C, (Wellington).-With a transfor- * mer 1$ x 14 should the primary be 850 turns of 22 enamel, and the secondary 80-gauge enamel, 870 turns , . A.: The primary is right, but the secondary will give approximately 200 volts, You should, use. a 280 rectifier, which will..require g. winding of 18-gauge. d.c.c,

wire, consisting of 19 turns. For the four yolts valves you will require two windings each of 16-gauge. wire, with 16 turns on each, For a dynamic speaker your best plan would be to have one with a high resistance field winding, and increase the number of turns on the secondary to allow for the drop in the speaker. This would mean that you would need to provide at least 250 volts, the drop in the speaker being approximately 50 volts. -Px4 (Hamilton).-Would loss of volume in a battery set be caused by a condenser having been burned out? A.: Yes; if a condenser were burnt out you would get a leakage from one of the tappings or no voltage at some particular point. This would cause weakness. 2. Are the valves suitable, using A415 as detector and in the last stage? A.: A415 used as a detector is excellent. In the last stage, although it will give a high lift, it is not really suitable for that socket, and you should use one of the B406 class, which will give you much improved results as far as tone is concerned, 8. Would it be the "B" batteries wrongly connected that cause loss‘ of volume and skipping oscillation ? Ac: Yes. If the "B" batteries were wrangly connected these symptoms would manY¥fest. themselves. It sounds, too, as though your set is not now neutralised. As a matter of fact, your set was designed for the 119 types of valves, and unless it is very carefully re-neutralised it is not advisable to use any other type in it.

pUZ2ZLeD (Berhampore) : Reception is variable. Signals come in strongly and then die away. A.: It is impossible to say. The first thing. would be to measure the voltage of each of the valves when the set is in a quiet period and when it is normal. Make quite certain that there is no voltage fluctuation. Obviously, then, the trouble must be on the h.f. side. Have all the valves tested. 2. Can you tell me how to step my detector voltage down to 224? A.: Yes; connect in series with detector, tapping a variable resistance of 20,000 ohms and put a 1 mfd. by-pass condenser from the set side of this resistance to B-. You ean then regulate the voltage to any value you desire. 8. What bias is required on B205? A.: It depends upon the "B" voltage, but presuming you are using the full you will need from 15 to 18 volts. GUPERHET (Gisborne): Your best plan would be, if you cannot get satisfaction from your local man, to write direct to the N.Z. agents and make a complaint. The address is Spedding, Litd., Auckland. Certainly do not call in anyone else if you are protected by a guarantee, and if we were to tell you to interfere with your set yourself, you would likewise lose the guarantee. GPARKS (Wellington): Could you advise me how best to. obtain experience in order to get my radio serviceman’s examination? a: You first of all should study the fundamentals of radio in such a book as Henney’s Principles of Radio, or if you do not want to go as far as Henney takes you, get a general idea of the principles from the "Radio Guide," and in the "Radio Times." In them you will find many of the fundamentals explained from month to month. Certainly as far as the a.e. set is concerned we would recommend you to look back over the last two months and read the series now running. on the A.B.C. of the ac. set. The best servicing book that we know is "Radio Servicing," by Ghirardi, a book which is not particularly expensive. As far as the experience is concerned, you certainly need a fair amount of this before you would be eligible for a serviceman’s certificate. The requirements are that you be three years in the trade. However, by having your wireman’s registration you will be able to. install radio sets, and possibly you could make arrangements with some

of the local dealers for a small remuneration to fit in in some way in their service department and so obtain your experience. pea (Rotorua) : Is the suppression of noises through electrical supply by means of a filtering device satisfacs tory? A.: Where interference is bad and it is being picked up by the a.c. mains a suppressing device will have a great effect. We understand that these are not obtainable in New Zealand commercially, though they can be made up from specifications which have been given in the "Radio Record." 2. Explain the method of earthing the free end of the aerial for the purpose of suppressing rower line interference. A.: We do not know anything more about this than you do. A correspondent wrote to say he earthed the free end of his aerial, so presumably he ran a wire down from the distant end and grounded it. Other than giving you the advice we did last time, we can do nothing for you. Interference is one of the biggest problems that the radio listener has to face and it has nonplussed many a clever engineer.

NOvicE (Auckland) : How can I find | the place on my three dials to tune in a station on a given wavelength? A.: Only by a knowledge of your dials. For instance, you might know that 2YA, which operates on 420 metres, comes in at 80 on one dial, 81 on the other, and 79 on the third, and that 2BL, on 351 m., comes in, say, on 64, 65, and 68. You then would know that a station on a wavelength intermediate between these two points would come in somewhere between those dial readings. Otherwise, there is no other method. 2. Where could I obtain a book from which I could get a working knowledge of radio to build a set myself? A.: We can do little more than recommend our "Radio Guide," which is obtainable from all booksellers in New Zealand for 2/6. DEE STREET (Invercargill): I have tried out two sets in my shop, which is near the tramlines, but the interference from trams is very considerable and reception is unsatisfactory. What can 0? A.: There is very little you can do. Interference is one of the bugbears of radio, and you are very near a tramline. Keep your aerial as short as possible, and have it at right angles to the tramlines. You are in a_particularly bad place, as there is a loop in the line just by, and that would cause a fair amount of noise, which would probably be fed in through the mains. Try an interference filter if you can get one, ee (Buller): Which line of figures is used for each class of battery "A? 6B" and "C’ on my meter? A.: The lowest range is for the "A" battery, the next range for the "B," while the "C" can be tested either on the "A" if it is of low value or on the "Cc" if it is of high value. The top one measures current and must be used only in series with the lead through which the drain is to be ascertained, 2. Can the valves be tested with a voltmeter? If so, how? A.: You can test them with your milliammeter providing they take the large current, but as you are using a battery set, the valves of which do not take much eurrent, the scale is too coarse. You would need a 0-20 milliammeter at the most to test your valves satisfactorily. On your meter there must be four terminals. one for the negative. one for the milliamps, another for the high scale (volts 160). and the other for the low scale (volts 8). To test your "A" and "O" batteries, have one at the negative and one at yolts 8. To test the "B" one at negative and the other at volts 160. You will probably not need (Continued on page 28.)

rom. Questions and Answers (Continued from page 17.) t® use the milliamps, but if you do, you connect one to negative and one to milli- ' amps, R4d!I0 (Stratford): Your alterations are in order, and except the use of a Imfd. condenser between the plate of the first audio valve and earth. If you did this you would cut out all signals, If you want to by-pass the jack, by-pass the oh to earth. ould a 200 henries audio impedase be high enough to spoil operation? 7 A.: No, it would be quite satisfacory.

3. Can you give me details for making coils for the broadcast band? A.: These have been published many. times, and we advise you to look up some of the back issues of the "Radio Record" or the "Radio Guide." A table is piven in the 1930 "Guide" which should help you to design your own. J ACKO (Otahuhu): I have built the "Sparrow Hawk" One and have been successful in logging the Auckland sta tions, but have not yet been able to get any other shortwave stations. There appear to be dead spots on the dial. A.: To remove the dead spots, take a few turns off the primary coil, and you will find then that the set will oscillate more readily, and you will be able to get further afield. Wailing that,

try. different -valued condensers in the oatal. The usual value is about 2. Why ean I receive better when my battery is almost discharged rather than when it is in full voltage? A.: Because your valves work better at a slightly lower potential than their rated value. Incorporate a resistance in the "AL" or "A-" lead and so control the voltage to the valves. You will then get better results, . ‘8. Can I use phones on my set without damaging them? A.: It would be unwise to do so. You would need-an output filter. R %. (New Plymouth): I have been * unable to get the "Neutron Four" to function. What is "T" of the regeneraformer? It appears from one diagram and in the text to be the top of the primary coil, and in the other the top of the regeneraformer. A.; "T," as is shown quite clearly in the regeneraformer diagram, is the top of the tickler coil. If you look more closely into the bottom sketch you will see that "IT" is not the top of the primary, but that the dotted lines extend beyond the last line representing the primary coil, On page 18, third column, six lines from the bottom, the "J" position should read the "P" position. A line has been dropped in the first column, under the second para+ graph of page 21 under the heading "Under Baseboard Wiring." The paragraph should read:"A connection’ is taken from this point (the F- terminal of the detector socket and the moving plates of the detector condenser) down through bole number 5, along underneath the baseboard to hole number 6, where it connects with F of the regeneraformer. A connection is made between this point and one lug of the 1 mfd. condenser." Yes; "N"’ and "end" are synonymous. Why .you cannot get the set to go is & puzzle; we have known several who have constructed and have had great results, e.g., see a letter in this month’s "Log." We have built it ourselves and it is giving excellent service. Try to locate your trouble. Put your finger on the grid-leak and see if you get a bugzing in the speaker. If you do not, there is something wrong in the audio system and this should be checked over. Pull the power valve out and see if you get a plop in the speaker. Probably you will. Go back to the first audio, pull this out, and you should hear the contact being made. If the andio system is all right, bring the aerial in to the fixed plates of the detector valve and see if you can pick up anything. This would indicate a fault in the r.f. stage. Therefore the only way is to make a systematic search of your receiver until you find the trouble. The circuit is a really good one, and, apart from the two small inaccuracies which do not seem to have worried many people, no difficulty has been found in the construction of the set. B.L.S. (Bombay): Is it necessary te show one’s method in arriving at an answer to questions such as the first on page 29 of the "Radio Times"? For instance, I work by a slightly different method from you, and arrive at the same answer. A.: Unless the method is specifically asked for, there is no limitation as to which one will be employed. The one used by us is the more usual for twe resistances in parallel, or two-.capaci- ties in series. However, it is exactly the same as the one you use, only we have taken it a step further,

2. How do you arrive at 6 mils from the equation x 1,000-evidently 5, a pritters’s error. A.: Yes; by reading the context it is 21 quite obvious that it should be ohms. We think, however, very few would go wrong ovér this point. It is really quite a small one. Nevertheless we are véry sorry it crept in. 8. How often will the Servicemen’s Examination be held? A.: We understand that it is to be held twice yearly. 4. What do you consider to be 4 good publication for intending setvicemen? A.: There are many publications that ‘will. help to obtain a real understanding of service work. One of the best we have comme across is Ghirardi’s "Radio Servicing Course." Another good book is "Testing Radio Sets," by Raynér. Another, "Servicing the Superheterodyne" by Ryder, and for general understanding of the principles of radio Henney’s "Principles of Radio." el SJ (Lower Hutt). I cannot cut out Wellington on my "Neuton Four." It spreads practically all over the place, and I get 2Z2W at about 10, 8YA comes in at 19, while the Aus tralians of note cannot be heard while 2YA is on the air. I get the best results in the locals by using aerial No. 1, shifting off the radio frequency valve. I put a .002 condenser in the aerial, but it only made a slight difference. How can I sharpen the selectivity? A.: Selectivity can usually be improved by increasing the grid bias on the first valve. However, this should not need to be greater than 7.5 volts. Selectivity to a large extent depends upon the aerial and the way the coils are made, and this explains possibly why we were able to eliminate 2YA and bring in the other stations nearby without any difficulty. A .002 mfd. condenser in the aerial is much too large. Try a .0002, or even a 0001 mfd. However, if you cannot get the set to work properly, use 4 wavetrap between the aerial and the set and cut out 2YA by that. Probably you have some of your old parts, and could quite easily make the trap up without further expenditure.

Prim- Secon- Re- Band. arY a davy. Wire. aetion. Wire: 9-16 32 26.d.8.�. 8 30.d.8,0. 15-28 3 26.d.8.C. 62 g0d.S.c 15-28 8 26.d.8.8. 5} 30.d.8,&, 28-50 26.d,.� 10 godg,e 50-100 18 26,4.9.C. 113 30.d,8.0