QUESTIONS AND ANSWERS

Radio Record, Volume V, Issue 35, 11 March 1932, Page 12

QUESTIONS AND ANSWERS

FRANK

KEE

X12HB (Havelock North): I have been using 230 type valves made by and I am changing to the same type nade by Y. Will it be mecessary to reneutralise the set?-No. 2. Would a valve of the same make but with a burnt-out filament do to plug in the r.f. socket when neutralising?-Yes. 8. Must a. Beverage aerial be in a aight line from the aerial terminal of ; set, or can there be an angle with a ghort lead to the set? A.: The lead in can come away at an angle. It is not absolutely necessary that the Beverage aerial be run in a direct gtraight line. PO RA PAAAAS ST OY

S J.W.S. (Invercargill): A description \"* of the short-wave adapter appeared in the 1930 "Guide." The superhet. type appeared in the 1931. "Guide," and it is likely there will be an adapter in the 1932 "Guide." Your set is quite a well-known one for dxing ability. (CURIOUS (Timaru): We regret we cannot supply circuits. If you will look through your back numbers you will probably find one fairly close to what you require. A s.g. set, if properly adapted, will not radiate. NEW CHUM (Dunedin) : 250 volts are quite suitable on the plates of 245 valves, Yes, the transformers will be suitable, but we cannot make comparisons between makes, You could use the inductor dynamic speaker with the "Radioram." J B.G. (Hamner Springs): All four * valve sets are very broadly tuned. The Shielded Five would: certainly be better, but we should advise you to wait for the new four-valve set which will appear in the "Radio Guide." The Shielded Five is rather out of date. PLS OO LOOK x KOOOO MAAAZS

MeLtrmMu (Otago) : Will I be doing any harm by taking an extension speaker direct from the plates of a valye? A.: No, but it would be a better plan to take the lead from the plates of the valve through an output transformer and then on to your extension speaker.. By doing that you would prevent direct eurrent flowing through the wiring of your house, which is wasteful and for that matter dangerous, but when you come to the voice coils you are past the 25-1 step-down transformer, and it is no wonder that the reproduction is weak. Transformers do not always strengthen signals. A certain amount of matching must take place before any improvement is noticeable. However, by using the transformer you are keeping back the plate current from flowing in the extension wire, which is desirable. C B.R..(Temuka): A half amp trickle * charger would certainly not shorten the life of your battery. If anything, it should lengthen it, because you are charging constantly at a low rate, which is advisable. You have probably struck a bad battery and have been unfortunate. (CRONA (Napier): A noise similar to static has developed in my set. It is still present when I take out the two r.f. valves. A.: Take out the detector valve and see if it stops; go on from that to the audio valve and you will find out exactly in which place it is, It is probably due to a broken-down condenser or & ‘defective transformer. The trouble may possibly be in a valve itself. Are you quite certain that all your connections are solid. G P. (New Plymouth): In my _ five- * yalve set I am using four PM6’s and one A615 as detector. Is that a good combination? . A.: We wish you had heard our ejaculation when we read your question. The answer is no, no, no. In fact, we think you could not have found a worse combination. PM6 is a power valve: How long do your batteries last, two weeks? You should use 221’s in all stages, except the last, where you use a PM6, A615 would be quite satisfactory for detector. 2. I pick up a great deal of noise from the trams. Is there any way of mitigating the noise? A.: In reality there is very little you can do. See that your aerial is at right angles to the power noises; try a different earth, and if necessary use a shielded lead-in wire. 3. My aerial has been up for four years. Would it be to my advantage to erect a new one? A.: We doubt it, providing corrosion has not taken place and your insulators are reasonably clean. R4010 Trician (Te Awamutu) : When and in what centre nearest Te Awamutu will the next radio serviceman’s examination be held? A.: That is more than we can tell you. Full particulars will be announced in the "R.R." when they are available. 2. What conditions or regulations have to be complied with in enterine for the exam,? A. Before you can be granted a certification you must have had three years’ experience in radio as a trade or professionally, and be cognisant of the regulations appertaining to the installation of radio sets as well as the technical practice entering into their servicing:

3, Where can the syllabus be obtained? A.: Write the Registrar, Radio Serviceman Examination, ¢/o the New Zealand Fimployers’ Federation, The Terracé, Wellington. We are sorry we cannot give names "and models of sets, as, although there would be certain advantages from the reader‘s point of view in doing 30, there is always a possibility of trouble so far as the trade is concerned. R00 (Wellington): Would a sevenvalve super het. be better than a ninevalve for dx work? A.: We see no reason why it should. 2. If an electric set earths through the mains, should it have a separate earth? A.: Try it with a separate earth. Sometimes it will go better, 8. My lead-in is three feet from a stray wire. Would this have any effect on re-ception?-Probably not. A H.S. (8S. Cant.): Writes regarding * an inquiry of D.C.D. (Auckland), stating that the circuit he required appeared in "Wireless. Weekly" of November 27, 1931. A B.S. (Rewa): On adding another * audio stage my set squeals. Removing "C-1’? improves matters slighty. A.: Take the grid bias battery into the set itself and so shorten the gridlead. Your layout is not of the best. Probably this alteration will clear things up. Try revérsing the primary connections to the second audio transformer. Your aerial system appears to be quite satisfactory. H A.I. (Hamilton): No. The. circuit for extra stage of an rf. s.g. for the "Radiogram Five" has not been published. If you wish for it, however, we shall post it to you. It is not a

Information Coupon (To -be used with all requests for information.) Name of set ..... as eceescccoeseses if Number of valves aeceseseseseeecess , Name Pome ee sreeesHesesereseseeesse Address Coeesccessseseeeseeeessess POO S ee Oe Ce EOS SOTEO OSES ESOESOSESEL ONES Nom de plume weerovcrcsaseoeses® To be kept in subsequent inquiries. Date ceseccccccccecccnvceseces Please Note:(1) Frc specific . and brief, tabuting, if possible (2) legibly, and on one side of the paper. (3) We do not design circuits, but accept suggestions for feature articles.

practical proposition to use an a.e. valve for a shortwave battery set. 2, What alteration is necessary to use »201A valves in a two-stage r.f. B.D. re- * ¢elver, now using 199 valves?: 22 y re-neutralisation. 221 valves, but 221 valves will be better than 201A’s. N=2=w STARTHR (Payparoa) :. We cannot understand why you can only get outside of New Zealand and not New Zealand stations, Surely you have made your difficulty not quite clear, and as it is We cannot give you the information you require. You should contact the dealer who sold you the set, MSK (Whakatane) : Your easiest plan is to find the speaker voice coil leads to the output transformer: and put a Switch in one of these. When = you use your phones, cut the speaker out by means of a switch. There is no need to worry about the field coil of a speaker. If you cut that out you will probably render your circuit: inoperative, If the output transformer is at the speaker, you must break the speaker side of the transformer, OX (Otahuhu).-I have a 100ft. aerial * 40 feet high, and have found my superhet very selective Would I improve sensitivity if I used a longer aerial, still maintaining the same height? A.: In all probablity, yes. Super-hets. are very selective, and a long aerial will have very little broadening effect on the tuning. However, you will probably brig in far more noise if you use a longer aerial. 2. My valves require renewing. Would it be possible to substitute some of the screen grid valves, such as the multi-mus and pentode? A.: No. The set must be specially designed for these valves to incorporate them. Alterations would be more than slight, and would certainly not be worth while. 4, You could have a phones connection made, but it is doubtful whether it would ‘greatly increase the range, as you would bring up the noise level, nnection would be neither costly nor dangerous. 6. It is unlikely that altering the aerial and earth terminals would have any effect on your set. They will probably do the . job you want done perfectly satisfactorily. 7. There is a slight hum in the transformer. I put this down to a loose lamination, and had the transformer repaired, but have noticed it again. Could you suggest a remedy? ; A.: Quite frequently this is due to design, and at other times to small faults in manufacture, but provided it does not interfere with your reception, it is not worth worrying about. M R.G. (Wellington).It is questionable ° whether the P. and T. Department would pass your adapter. Being of the autodyne type, and directly coupled at the aerial, it would be a very prolific source of oscillation. In fact you could almost call it a small transmitter,. It would not improve the "Kestrel Three." 2. A differential condenser would be of little value; an earth connection is usually unnecessary with a _ shortwave adapter. . ; 3, Yes; by broadcast you . make jt into a super het. C.C. (Hanmer Springs)-Could I * use the parts of my 5-valye commercial set to build the Super Six? . A.: You could use those parts are suitable. ; 2. You could use your d.c. quite satisfactorily for the "S.S." ; 3. We regret we cannot publish for the coils as they would certainly occasion you great difficulty in manufacture, AYBACK.-TI have an old battery set 2 of six valves. What is their desig\nation from left to right? A.: Had you told us your model we could have been more exact in our reply. However. it is probable that the first three are radio frequency followed by the detector, first audio and power valve. The last one should, by the way, be a power or semipower valve (B605 class), not A609. BG60S

would require to be biased. by about 9 to 12 volts, depending upon your "B" voltage, 2. The set is clear in daylight, and not so at night. Why? A.: It is due to your locality and not to your set. iD H. (Rotowaro).-Try Johns, Ltd.,. ‘Auckland, or Fear, Wellington, HAS. (Auckland).-I have built a choke, but this cuts the yolume down about 50 per cent. Is this correct? A.: Certainly not, but you haven’t given enough particulars to let us know exactly to locate the fault. Probably your choke: has too high a resistance, 2. Would a small dynamic speaker be as effective as a cone speaker A.: Yes; modern dynamie speakers are quite as efficient as cone speakers unless the latter are of a very light type. A dynamic speaker would give you much better quality, although if you do not have full yoltage and a power valye you would not get all that the speaker is capable of delivering, Foxy (Hokitika).-During the last week or so my set has become jumpy and noisy. I cannot turn up the volume without introducing mushiness, also the set is generally much weaker. A.: There are many things that can be at fault. The "quality" condenser across the last transformer may have broken down; the grid resistance in any stage may have gone; one of the coupling resistances between. the detector and the first audio may have brokén down, or a resistance for that matter in any part of the set may be giving trouble, It is really a case of calling in a serviceman. 107 (Waipukurau).-We think the orthodox aerial would be the better. The fact that you propose taking a lead-in from a point other than the centre would materially offset any other advantages that the proposed aerial would possess. . SUPER (Taranaki)-In building the "Cathode Super," using battery valves, should I wire the 15,000 resistance in series with the oscillator lead, and connect it to the grid return, or how should it be connected ? A.: The method of coupling the osciliator employed in the "Cathode Super" can not be employed with battery valves, and will have to be placed by a feed to a pickup coil coupled to the coil tuning the first detector, Any standard superheterodyne circuit will show the arrangement. The change, of course, to a great extent spoils the performance, as a short-wave receiver, although we. believe that with 2 certain amount of experiment the same excellent results as are obtained with the original arrangement could be achieved with this method also. 2. Using 135 volts "B" eliminator, what value of resistance should I use? A.: As with a battery receiver grid bias must be separately obtained from batteries, the biasing resistors leading the various cathodes to earth should be dispensed with altogether. The screen and plate resistances may remain the same, or may, if desired, be slightly reduced all round to compensate for the lower voltage available, & Hither 200 or 250 turn coils may be used, 4, The primary turns are 40, although the addition of four turns will make not the slightest difference. W.T.N. (Ward).-What is the voltage * supplied to the radio frequency part of the set by the power pack? A,: 180 volts-current about 20 to 25 milliamps depending on the particular valves employed. 2. Instead of honeycomb coils could one make a band-pass filter by winding the primaries and secondaries so that one would fit within the other? . A.: No doubt satisfactory filters could be constructed on these lines, but the particular mode of construction suggested is likely to result in the coupling being much too great. Under these circumstances the band-pass effect will almost certainly degenerate into an altogether objectionable ouble-hump resonance curve. Why not (Concluded on page 23.)

Questions and Answers

(Concluded on page 13.) bank-wind the two coils on the oné former, keeping them separated by one and‘a hait inches or so? JAN (Christchurch). -Would it be satisfactory to work the "Cathode Super" as far as the second détector from a standard powerpack without reducing the value of the anode résistance and tHose for the screen and grid bias? I have a powerpack which will deliver up to 250 yolts, 100 mamps. A.: Yes. As a matter -fact, its initial testing was done under these. circum--gtaneces, when American and Japanese stations were tuned in on a speaker. Naturally the volume cannot be made too great without introducing distortion. The yoltage on the 224 valves is no higher than usual | . 2. I have two audio amplifiers, one used in push-pull, and the other incorporating the Loftin-White. Which do you consider to be the most suitable for the super-het? A.: The push-pull amplifier would be decidedly better, although either might be used successfully. M M.M. (Auckland): Your circuit ap- * pears to be correct, and it seems that you are not getting the best results because your condensers are out of — step. Try first of all the effect of balancing condensers, and if they improve things in any way, adjust the coils until you get the condensers in step. With two stages of sereen-grid you. should get really good results. . TENODE (Wellington): As fat-as we can see; no damage is being done when your eliminator stops. * 2. We think that type of rectifier suitable for your needs is not available in New Zealand at the présent. time.