Questions and answers

Radio Record, Volume IV, Issue 24, 26 December 1930, Page 13

Questions and answers

"TIGHT" (Christchurch): The primary of my L.W. power transformer has a break in it, but the secondary and filament wires are intact, Could I wind another primary on the outside? . A.: Another primary on the outside in all probability not be satisfactory. In our laboratory experiments burnt out ¥

primaries are quite common,-and we find the best way is to remove all iron and lift off the spool end. It will be found that if care is taken they will come away quite easily without wires dropping. The primary then can be pulled out; another one can be carefully wound and slipped back in the place of the defective one. It is not necessary to place the spool ends back on the transformer again. Battery compound or wax can be run over the wires to protect them. ‘This operation is not a delicate one, although it requires a reasonable amount of care. We have’ done it many times; and never had a failure. 2, Can the secondary of the transformer be used as an output choke? A.: It could, but it would have a low inductance. "T)IH-HARD" (Seddonville): What is > the best valve combination for my A.: Four 221’s or 201A’s, and one semihigh gain power valve of the B605 or UX 112A type. 2. I cannot get any station before 8 p.m., and there is a continuous crackling in the set. A.: This sounds like a defective transformer. Have these tested (you could do it yourself by the phones and cell method, so frequently described in these columns). Try another grid-leak and tug the joints for dry or loose connections. M E. (Nelson): I have connected the * wire from the Daniells cell charger and the lead to the set to the same battery clip. Am I not putting excess voltage on my valves? . A.: There should be two wires from the charger and two from the battery. As we pointed out before, this excess voltage is cut down by the parallel battery. However, if you do not feel too sure about the connections take an ordinary torch bulb and connect one wire to the screw thread and one to the soldered tip. Place these across the filament terminals of one of the sockets and remove all the valves. Now turn on your set. If the torch bulb is the same voltage as your valves on #-volt below, it should light brightly, but if you have excess voltage it will burn out. In practice we have found that the charger does not affect the voltage of the set. However, it will be an easy matter to borrow a voltmeter. 2. If I have to connect the wire from the charger separately how am I to connect it to the terminals? ‘There is no room for another battery clip so far as I can see, A.: There is no need for the extra room if you want to connect the battery charger when the set is not operating. Take off the clips from the set and put the clips of the charger on the terminals to which the set clips were attached. 8. Would it keep my 30 amp. accumulator fully charged if I disconnected it when the set is working? It consumes just: over one-fourth of an amp.-yYes, 4, When I turn the set on there is a loud roaring noise which continues when, the aerial was disconnected. In a short time this cleared up. Would this be the result. of adding fresh bluestone to the charger? A.: It is most unlikely that that was the cause, but without further particulars it would be impossible to say. If it has stopped the cause is now immaterial,

O ©. (Mataura): Can a pick-up and ~* short-wave adapter be added to my six-yalve set? A.: Yes; the pick-up can be taken in at the detector valve by using a special adapter, if special pick-up terminals are not provided. Short-wave adapter either of the super-het. type described a little time back or the type that is going to be described in the 1931 "Guide" would be suitable. G M. (Auckland): My four-valve B.D. * works better by reversing the wiring to B- and A-+ and by placing a 001 condenser across the primary of the first audio and the by-pass condenser of .1 mfd. from B+ rf. to A-+-+, Does the set use more B battery this way? A.: Providing your set is working well you are not bringing any trouble upon yourself, It will not use more B battery by making the alterations you suggest, as they are quite in order. Note: We looked in your letter quite a long time for a coupon, but could not find one. We presume it dropped out in the post, "QIMPLEX" (N. Auckland): What is the number of r.p.m. of talkie sound discs ?-83.1/38. 2. What is the correct film footage per minute per revolution of the disc? There cannot be a film footage per minute per revolution. The normal speed is 90 feet per minute. Film footage per revolution would be this number divided by 33 1-3. 8, What is the correct gear ratio to give me correct dise speed? A.: There are too many factors, depending on your equipment, for us to discuss this. Your best plan would be to study the periodical "Projection Engineering." You should be able to obtain a copy from the Te Aro Book Depot, W. (Hamilton): I have an electric * receiver which uses the mains for an aerial. Every time a switch is turned on or the automatic telephone rings a buzz comes through. What can 0? A.: The best plan would be to use a separate aerial and earth. This would probably get over most of your trouble. Probably a very impromptu aerial, such as the spring mattress of a bed, would be sufficient. 2. There is a welding plant in the vicinity. Would this cause a continual click followed every two or three minutes by a harsh grating sound?

A.: It sounds very much like it, and it would not be a bad idea to see if anyone in that vicinity suffers with it. If anyone in the locality of the Waikato Hospital, Hamilton, should read this note and has any comments to pass about any similar interference we ‘would be only too pleased to publish it for your benéfit. M. (Otorohanga): Tuning in my * six-valve set is very flat. Could I use a better valve combination? I am using a 201A in all stages except detector, in which I am using a PM.6. A.: Are you sure your PM.6 is not in the power stage, for that is where it should be? ‘Trace out the wiring from the plate and it should go to the speaker, or, better still, if you cannot recognise the plate wire, trace back from your speaker terminals and you will find one goes to the B battery and one goes to the power valve, ‘This should be PM.6, with a bias of about 9 volts. HowCoFRDSPONDENTS must attach this coupon to all queries sent to the Technical Editor (Box 1032, Wellington). Questions arriving without it are likely to go astray or be delayed. . Name of set ..... cccccccavescoacce Number of Vales .ocecscccassecose Name. ..secee occcvccececececcenscn AGAreSS cocccevcvccccecccesssonsce eerecesoe SP POHLEBHO SO OCOHEESESREEZEBOOD Nom de plume .vcccccocscvsceecce To be kept in subsequent inquiries. Date Coccccccescncccccccceuces Please Note :- (1) Be specific and brief, tabulating, if possible. (2) Write legibly, and on one side of the paper. (8) 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.

ever, for quality PM256 would be better. It would need a higher bias, ‘You cannot do much to improve the flat tuning, but you could try a formo-densor in series with the aerial, varying the capacity for the best effect. 2. Could you recommend any correspondence school or person who would give me a little practical instruction in radio, and is there any book on sale which would explain the radio terms? A.: You could receive instruction from Johnson’s Wireless School, Wellington, .and you would find the "Radio Listeners’ Guide" a good help for learning the terms. The 1981 publication is on the way now. "TNATRY" (Palmerston North): Resulis .™, are disappointing when my fourvalve B.D. set is used with an inductor dynamic speaker. A horn speaker goes splendidly with easily twice as much yolume. A.: Have you had the inductor dyna‘mic speaker and your own tested on another set? The comparison should be interesting and will tell you more than .you can find out by experimenting with your own set, 2. Will the baffle 2ft. Sin. x 2ft. have anything to do with the efficiency? A.: No, the tone will be affected slightly, but that is all. . The baffle is quite efficient. F 3. Are 90 volts sufficient? A.: No; to get the best of tone from the inductor dynamic you need 125 volis at the least. " NOTH.-"‘I am quite agreeable to wait a week or so if. you have a large batch of inquiries," says our correspondent. Thank you very much. We wish

all our correspondents would adopt the same attitude. Quite a number get quite annoyed if they do not receive an answer in a week when, especially at this time of the year, replies are likely to be held up. "RADIO-STULTERS" (Southland) . The speaker appears to stutter, but the eliminator still hums and I get a squeal from the grid-leak when touched, If I turn the set off and then on again it goes all right for a while, and then repeats the performance. It goes quite satisfactorily at night. A.: We cannot understand why it should go all right at night and not during the day. On the surface the trouble appears to be in the radio stages. — It may be a fault in the radio plugging from your eliminator. Possibly there is a broken down or defective condenser there. Concentrate upon the _ radio frequency stages and look for defective or dry joints, loose connections, valve pins not making proper contact. Try bringing the aerial into the grid of the grid-leak. If this set works satisfac. torily in this division, then the trouble is definitely in the radio stages, T.C. (Wellington): What is your *. opinion of the enclosed circuit? A.: We cannot tell; you have sent the theoretical diagram but not the layout. If you want a real good set build the Differential One or Two, which we will be describing this and next week. 2, Will a five to one and a three to one transformer be satisfactory? A.: Yes; use the five to one for the last stage. 8. Would the valves be satisfactory, two L210, and P215?-yYes.

4, What would be the resistances in ohms. ? ‘A.: Which resistances? If the impedances of the valves L210 is 12,000 and P215, 5000. ; J E.W. (Lower Hutt): What power * pack voltage is needed to supply the L.W. with two 245 valves in parallel? A.: The same as for a single 245, that is 425 volts, but your power pack must be capable of supplying 60 mamps, 2. What is the actual voltage on the plates of the 245’s after allowing for the voltage drop to the 245?

A.: There are 250 volts or thereabouts on the plate of the 245’s, and 180 on the screen grid plate. 3. Could I use Ferranti wire wound resistances so long as they were of the value specified ? . Yes, providing they will pass 60 mamps. 4. Should there be a condenser between the ‘arm of the potentiometer and the cathode of the screen-grid valve? A.: Yes; it was inadvertently missed out by our draughtsman. It is the same as for the single 245 output valve. 5. What is the value of the blocking condenser in the primary lead of the cutput transformer? A.: 2 mfds. 6. I take it that the parallel circuit is quite safe to build and is practical and not theoretical? A.: It is perfectly safe, for it is practical as well as theoretical. "DENTACOLL" (Dunedin): I am troubled with crackling in my set, and I have tried almost everything, including changing the transformer to eliminator. This occurs when the aerial and the earth is not being used. I am using a home-built eliminator. A.: You seem to have tackled all the usual troubles and we are really at a loss to give you any help.. The C battery could cause the trouble, and we presume you have tried replacement. Furthermore, the first stage jack is not past giving trouble. Cut it out of the circuit altogether and then try it. The C- voltage should not be equal on.both valves. Try the eliminator on another set. It may be a troublesome condenser in that. Failing all these, rebuild the set along modern lines. It is really very old-fashioned. 2. What six-volt valves should I use? A.: Use a g.p. valve in the rf. and first a.f. stages, a special detector, and & power valve of the 605 type. "PD ADIO" (Shannon): I wish to. construct temporary resistances in cardboard, Could you give me the dimensions?

--e A.: We had quite a good deal to say about this when we were describing the "Home-made Three" in our issue of December 6 last year. From this description you should be able to. manufacture your resistances without any difficulty. | R H. (Avondale): I submit a sketch of * two alternate situations for an aerial. Which do you think would be the better? A.: The second aerial (the one you have marked "D"). It is more direct and does not pass over the house. Furthermore, your lead-in would be shorter,

2. I have not been able to get any Australian stations yet. You have not stated the type of set you are using. In any case Australian. stations are very weak at the time. They cannot be picked up until very late at night, and even then they are not very satisfactory. 3. What is the significance of the dial numbers? A.: They are only degrees of a circle, and have no connection with the frequeney or wavelength. 4. My set has a tendency to whistle or growl. ‘ A.: If this is the ease you should contact the dealer from whom you bought it. Some commercial sets will do this if forced, but it should not be strong enough to interfere with the tuning. 5. Is there any literature available on the number of stations and their whereabout&, and what is the best radio book for a beginner to buy? A.: You will tind the "isteners’ Guide" is an excellent publication on both these scores. The 1930 has been sold out, and the 1931 is in preparation. It shoul be out in the beginning of April, 6. Should the aerial be continuove™to the set or the lead-in soldered to the aerial? ° A.: It would be better continuous. A B. (Wellington): Where can I ob5 * tain a copy of the R.R. of March 7 A.: If you cannot get one from a bookstall you can get it from our office, 2. I have built R. the W. Three, but I ean only pick up two American stations, . A.:You should be able to do better than this as most of our correspondents have been able to get a very wide range. Try increasing the detector or use another valve in this position. Try the effect of, a higher grid-leak. I am about three hundred yards from a very high hill. Would this cause poor reception of American stations? A.: In all probability, yes. Hills have peculiar effects upon reception, and one

not infrequently finds that a shadow can be cast right across the aerial to completely spoil reception of stations in the shielded direction. "PHACTION" (Nelson): Will the iron ~ I have on hand, the dimensions of I give, be suitable for a small audio choke? How. many turns: of 40 or 36 gauge wire will be used? A.: Use 40 gauge-and you will require about 3/5lb. The gap should be about -03. Wind on all this wire, which should take up most of the space available. Actually you need about 15,000 turns. 2. What is the dielectric constant of paraffin paper of medium weight? Will it stand-150 volts? A.: Dielectric constant 2 to 2.5. It should stand 150 volts. *"ATORTH-WEST" (Rawene): We cannot get any result when the short~ wave adapter is plugged into the second: valve socket of my 1926 model H.R. A.: There is.probably something wrong vith your adapter because the plug-in to thé’ valve socket should act quite well. It‘would not be a bad plan to have your set brought up to date, 2. Why do we have space-wound coils for both long and short wave .: These are really most efficient coils though the modern practice is to make them smaller and sacrifice some of the efficiency for the sake of neatness and convenience. Valves now are more efficient than they were in those days, consequently a little loss in the coils can be tolerated. 8.. Would a small coil be used to tune the adapter in a similar way to the one in the broadcast set? If so, what are the specifications? .: We cannot quite see the point of your question, The adapter should have a set of short-wave coils which are plugged in according to the waveband required, There should be no need to interfere with the broadcast coils. 9 4, Would the distance between coils required to be altered for the different wavebands ?-No. "DAROLE" (Oamaru).-Does a sagging serial affect results? A.: Slight sagging does not have any effect upon results, but where it sags sufficiently to cause sway. artificial fading quite frequently results. It is more noticeable on short-wave, : . My lead-in runs back from the set. Is this ‘efficient? A.: It would be more efficient if it ran forward under the aerial. However, it is quite a small point. 8. The earthwire is of fine copper, and is connected to the waterpipe underneath the house. ‘Is this efficient? . A.: The wire should not be very fine; in fact, it should not be less than 14 gauge

copper, or better still, stranded wire. It should be tightly affixed to the water pipe (soldered if possible), and preferably. the ground round about it should be damp. 4, Occasionally there is a crackling in my set. How can it be remedied? It may. be due to interference. Remove the aerial, and see if it persists. If not, you have no control over the cause, except to let your radio inspector know. Tf it does, one of your valves, probably the detector, is at fault. "T\XPHRIMENTER" (Nelson).-TI have been saving up the following questions for the past two months, They are sixteen in number. +A. : What about sending them in every week? They would be easier for us to handle. .

1. Does a tuned aerial circuit consist merely of a condenser across the coil? A.: The condenser is really across the primary coil. In: its simplest form a tuned aerial circuit consists of two coils, one between the aerial and the earth (this is the primary), and the other (the secondary) close to it, but not in contact with it. It is across this secondary coil that the condenser, is usually shunted. A sketch shows a good example. of a tuned aerial circuit. Will thin wire be better than thick for shortwave coils? A. Thick wire is generally the better for shortwave, and slot -wound primaries are rarely, if ever, used. 8. How is the Beverage aerial erected and is it better than 100 feet aerial 30 feet high? A.: Full instructions were given for this type of aerial a month or so ‘back. For stations to which it noints it is decidedly superior to the ordinary aerial. 4 hat is the best soil for an earth? A.: That question was fairly fully discussed about the middle of this year. Moist loamy earth, 5. Would an anode bend detector be better than a leaky grid for either broad- east or short-wave? A.: The anode bend would not be suitable for short-wave, but it gives good results on broadcast. 6. Would a battery of small Leclanche cells maintain a three-valve set drawing 10 m.amps. A.: Yes, if you built up a battery using for central elements the manganese and "carbon rod from an old eell you would get a battery which would keep your set charged indefinitely... 7. With my three-valve set I have -reeeived American stations on the broadeast. ‘Can Indian stations be received in New Zealand? : Yes, usually at about three o'clock in the morning. 8. If every component of a set were screened from the rest would it promote better efficiency? : In a set such as yours, no, 9, If a fixed three-coil tuner with condenser reaction was totally. screened would it make the reaction easier?-No. 10. Would two five to one transformers produce distortion or howl? A.: They would produce and in all probability howling, It ig .noi

"wise to use two high ratio transformers. .11,;. Should an ordinary two-valve amplifier with a pick-up give more volume than the average cabinet gramophone? A.: It will give slightly improved signal strength but greatly improved tone. _12. Would a pentode in the last stage give me more volume than a 112A using the: same plate voltage? A.: Yes, but generally speaking the pentode unless properly matched is not very satisfactory. A high gain power valve would be ‘-18. I have a erystal set which receives 2YA. Would a full-wave set give double the volume? Av: It is questionable. Some fullWave sets have given excellent results, while others have been most disappointing. Generally speaking it is a dubious éxperiment. . 14. ‘Where can I obtain particulars about amateur transmitting? A,: This week we are commencing a series of articles on that subject, 15. Where can I obtain the circuit of gn eight-valve Fada? _.A.: Try the National Dlectrie Engineering Co., Wellington. 16, Could any other valves be used to replace the two 171A’s in the above set _. A.: Not without"making several alterations in the power pack. E W. (Raukokore).-It seems to me that * with the Daniells cell charger the cells should not be connected directly to the set, as they are of higher voltage than the valve. A.: See our reply to a previous correspondent. , 2. I cannot receive any station during we day, but get good reception at night. y A.: This is quite. a seasonable complaint.. It is caused by the sunlight. Your locality may have something to do with it. 8. I can get nothing on the low wave except a broken buzz, which I take to be Morse. A.: This is probably Morse, and your failure to get telephony may be due either to your not having become accustomed to the set or to be detector voltage-being too low. Try removing the earth when searching for shortwave stations.

4. Would you suggest a change In my valve combination?-No, it is excellent. 5. L was told that it would be improved if I added a third B battery and a half a ©, but results have been inferior. The diagram shows the wiring and the alterations. A.: We cannot understand why this is. Your diagram is correct, only it would be better to use the full 9 volts C instead of the half battery. It may be an advantage to take the eonnection that usually goes from 674 to 90, instead of 112.5. It may be an improvement too, to bring the lowest tapping up to 45. "[TNTERFERENCE" (Blenheim) : During what hours can Morse amateurs operate their transmitters, and what wavelength are they allowed? A.: This subject will be fairly fully dealt with in a series of articles which commence this week. They can operate at any time and are confined to low wavelengths, Those who wish to go on to the broadeast wavelength must not operate during ordinary broadcast hours. Note: Your coupon was missing. "ENTHUSIAST" (N.P.): Could I use the super-het, short-wave adapter on my four-valve set?-Not satisfactorily. 2. Cam a stage of r.f. amplification be added to the adapter? A.: It would be a risky experiment for anyone who hus not had considerable practice in experimenting. 8. Would a better method be to ent out the audio stages and add an oscillator after the detector and use: this as an adapter in conjunction with a three sereen-grid valye set? A.: No, you are really looking for trouble in attempting an ambitious thing like this, Super-hets., although very

powerful, are not as easy to make as they appear, and to avoid disheartening readers we have. left them ‘alone in our columns, "T)IRECI" (Auck.): Do you know of’ any d.c, sets on the market? A.: ‘We do not happen to know of any particular makes, though it is possible that. Stewart-Warner might have one. ; 2. Are they dependable, as I am told | they are very hard on valves? A.: It would be, almost essential to have a voltmeter across the filament supply and this would have to be watched very carefully and -the voltage regulated, If this were done the. set would be no harder on valves than the battery or the a.c, set. 83. What type of set would you advise ‘me to use in the d.c. area? A.: Hither a good battery set with a B eliminator and a trickle charger, or an ac, set with a rotary converter. Probably one of the dealers would build one of the eliminator type to order ard you would operate it from the wall as you would an a.c. set, When you turned off the set the trickle. charger would be turned on automatically and you would not have to worry about charging batteries.. Of course both eliminator and trickle charger would have to be specially made, Another plan would be to have a d.c. set built up following out one of the circuits we published a short time -back. O ©.8. (Hamilton): Is my sketch of, * the Loftin Four with g 245 ‘im the last stage correct? me .: Yes, the amplifier end is the same.,. as for the Loftin Three. 2. Will a 280 be satisfactory with two 245’s in parallel? A.: Yes, but an Osram U8 would stand a higher voltage and perhaps it would _ be safer, . 3. Are two 245’s as good as a 250 ?-Yes.