Questions and answers

Radio Record, Volume V, Issue 10, 18 September 1931, Page 13

Questions and answers

P*6300 (Gore): I have a 7-valve set with an aerial 100ft. in length and 30ft. high, Could you suggest a better one? A.: Yes; get it up to 40 or 50 feet, using still the 100 feet span. Selectivity will be slightly impaired. 2,/How could I improve the selectivity? ; .: In a set such as yours the selectivity troubles can usually be traced to the condensers being out of alignment. This may also account for the slight insensitivity. If you cannot screw them up your‘self ask someone who knows something about the game to look at the set. 3. I have renewed all the valves except the 8 radio valves. Would they impair the reception or selectivity? A.: If they are still functioning satisfactorily, then they would affect neither. If the emission is slightly down both may be impaired. MATHUR (fe Kuiti)-I have ‘the original B.D. Four and was getting good results, although the set was not very selective, my serial being about 140 feet. When I use a 99 feet aerial the set squeals and distorts with the neutralising condenser right out. I have removed all "4

plates except one moving and one fixed, but the set is far more selective. If I connect the 75 feet and 90 feet aerials together and make a "IT" I can neutralise it all right, but cannot get beyond 2ZW, and the set ig very unselective. I am using three 221’s and a 112A, I-would like to get the set neutralised to the 99 feet aerial. A.: The best plan to adapt the B.D. to any particular aerial is to use a midget variable condenser in series with the aerial. You ean then adjust the aerial to the optimum length. ; O C.S. (Hamilton).-Will you give the * gauge of wire and length required for the field winding of a moving coil speaker-260-300 volts and about 80 amps? A.: For 2380 volts 30 mas. use 388 enamelled wire, 37,000 turns. ELECTRA (Anckland).--Sorry we left out the table referred to. It is published on the following page. . 1. Are the coils for a band pass crystal set connected up as shown? I find thal the set works quite as well with the coils shielded from one another. _ AL: There can be no justification for us‘ing a band pass filter in a crystal set, ,as it is difficult to see how it would be any improvement,

2. Does a band pass unit work well on shortwave using plug-in coils? A.: We have not tried it, and do not know of anyone who has, so we eannot answer your question. It is a significant fact that none of the commercial shortwave sets are made with band pass filters. Rock srmaLp (Auckland).-I want to add a further radio stage to my threevalve get. How can I do this? A.: A theoretical sketch was given in the "R.B." a few weeks.:ago under the heading, "Lhe Sereen Grid Valve," and it showed the most suitable hook-up for connecting an s.g. valve to a set. Your best plan would be to pull the set down and build up the Differential Four, or construct a set after that type. pD* 32HB (Napier).-I,wish to construct the "Outspan Five," and would like to know the following :- 1, The coil winding of the three coils using a .00025 condenser and a .0002 differential condenser for regeneration. A.: Using 26 d.s.c. wire you will need approximately 108 turns on the secondaries of each of the three coils. The primaries ghould be about 45 in each ease, the reaction about 60. The primary and the reaction coils should be wound with No. 28 or 30 d.s.c, wire. The valves you mention are quite suitable for the set except PM2 in the audio stage, Use a general purpose such a8 PM1. Yop may find that a special detector of the PM2DX type will go better than the R.C.C. valve as detector. LiS2tH0vsE (Nugget Point).-Will the circuit work satisfactorily with pushpull ag shown in the accompanying diagram ?-Yes. 2, What type of Philips six-volt valves should I use in the stages? A.: One A442, with 30 ohms fixed resistance in the filament to break the voltage down to four. In Meu of this you could use PM16, or some other six-volt s.g. valve. Detector, ACIS. First audio, A609, Pushpull, Bé05. 2 What should the ratio of the transformer be? A.! 33-1 throughout. Do not exceed this.

L.G@. (Raetihi).-I am using an xf. e tuner consisting of a s.g. valve and. triode connected to a detector. These are coupled into an A.C. amplifier, but every time the set is tuned to resonance, audio howl sets up. A.: On the surface it appears that the h.f, choking and by-passing is inadequate. Chokes should be situated in the following places: In the plate leads to both rf. valves, in the s.g. lead, By-pass condensers should be shunted between the chokes and the earth. A choke between the plate of the detector valve and the A.C. unit. The set side of this choke should be connected to the ground through a .0001 mfd, condenser.. These condensers should be connected to the A.C. point on the coils themselves, not merely acroas the battery. Is the shielding of your s.g. valve adequate? It should go right round the valve and! should be earthed. Try reversing the connections to the secondary coil of your 8.g. yalye stage, that is, to make the hig potential connection to the point of the coil that is nearest the ground and take the low potential connection from the upper end. This idea was explained fully when dealing with the "Kestrel Three." K A. B. (Pleasant Point).-What valves should be used in sockets 1-6 in my diagram? Iam using a five-valve battery se A.: We are afraid we cannot help you greatly. You have not given us much ata to work upon. Had you shown us at which side the dials wore and which end your speaker, we could have recognised

the valves. The valve nearest the speale? ig usually the power valve and this should be of the B605 class. All the others can be of the 221 type. . 2. Which of the two indicated on my sketch would be the better for an aerial, AB or AC? A.: We think AB the better, that is the way you have it at present. Hore on (Auckland).-It is evidently power interference, and it is not likely that anything can be done to improve the position unless you can locate the source of the noise. We think a Beyerage acrial would be no improvement. In fact it may make matters worse. APvANcs (Auckland).-If I build the "Advance" in its present form would the set be entirely satisfactory for broads cast as well as short wave? A.: Any all-wave set is designed primarily for short wave or for ong-wave operation. If you make a short-wave set into a long-wave one you are eompromising on the broadcast, and this is what happens with the "Advance." This set has shown itself capable of bringing the Australians and even odd American stations on the broadcast band, but it is not as good as a specially-desfgned longwave set would be. 2, Would variable condensers of greater capacity be more suitable if built for broadeast work? ‘A.: Yes, it would be adyisable to use larger condensers and smaller coils if the set is to be used for broadcast work, but then it would not be suitable for shortwave work. Generally speaking, .00035 condensers are quite satisfactory for broadcasting use. 3. What are the specifications for the coils tor a .00035 condenser for the Advance ae. set? A.: 2in, coils, 26 dsc. wire, secondaries 30 turns, primary 20 tickler 25 . 4, Alterations required for the power transformer where used for broadcast only A.: There is no alteration needed in he power transformer, but if you are wan P4

peer oa vero:ae (SORRESPONDENTS must attach this coupon to all queries sent to the Technical Editor (Box 1032, Wellington. Limit three questions, unless Jetter is accompanied by 2/ee. Name of set .....cevesseccvsvsovcs Number of valves ccccoccecevcsoneoe Name seeecoeso se sODoeoSOOpOSOSeOR Address 000 00008000008000 00 80 SRI90 PRTTTTITTT TT eee ee sacs Se eOBSOBODODOOOADOSHAGOB09 Nom de plume Sacre roeooeoeagseo® To be kept in subsequent inquiries. Date ceceeesecs-eecceeee ccccee 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 eorrespondence and while letters are given every consideration, answers are not necessarily ecorrect-they are only our opinion based un the matter supplied, which may be quite inadequate, Intricate and specifications cannot be supp without a specialixt’s fee. eae -wwt Si

te..uke the set for. broadcast only why not: huild up the "Radiogram Five" with an extra stage of 8.2. r.f.? DCTIFIER (Te Aroha).-Is the accom"panying cincuit correct for an elecWrolytie rectifier? A.: Yes, your circuit is correct, but if the "fire underwriters happen to see you using it, there. will be trouble. Such rectifiers are prohibited, eonsequently we cannot give you any details,

Bo02z (Hikurangi).-Crystal sets have been fairly fully dealt with in the "Radio Record" recently, and we regret that we cannot send you any further details by post. ~ G HB. (Auckland).-The "Rejecta" e Wavetrap was a great success until 1% A-caltered its frequency. Should I now tuke off some of the turns and stop double winding at the 27th turn? A.: Yes, that would be your better plan, and you would possibly then get better results. We note your request for a reprint of the d.c. article, but we cannot do this as space these days is very much a: a premium. Copies are still, available from our office. RAPaN (Dunedin).-My set develops a \v. very audible humming noise, which persists for three or four days. It then becomes so silent that qne does not know it is operating. The rectifier has seen about 4000 hours’ service. A.: We should certainly renew the rectifier, as troubles such as you complain of are very frequently caused by an aged rectifier. Failing this, communicate with the local agents of your set, whose service department will adjust it. ‘2. Which would be the better in the Loftin White amplifier, pushpull or a power pentode? : A.: The pushpull would give you a greater output.

8. Would the combination of the No. 2 Selectra Crystal set and a L.W. type of amplifier give as good a tone as is possible to obtain at present, providing all impedances were correctly matched and a good dynamic speaker used ?-Yes.

W H. (Wanganui).-Could my set be e made into an all-wave one; if not, could it be altered to give better results on distant stations? A.: From the plan you:have sent, it appears that it would not be easy to make your set into an all-wave one. If you wish to have one of these, pull the set down, using the parts to build up the "Differential Four,’ which was described in the "Radio Record" early this year. This should give you better results on distance. It would be better, too, for you to use different valves. Your detector valve should be a special detector, such as 2DX. The third PMi and the fourth PM2. PM2 does not have a high amplification factor, with the result that you are not getting the kick you should. 2. When I am listening to a distant or weak station, the set can be made to oscillate by 2a burst of static. A.: This is because you are working your set too near the point of oscillation. When a burst of static or a strong signal comes, the set goes over the verge of oscillation. It is very difficult to stop. this other than working a little back from the oscillation point. This, of course, would give you less sensitivity, but the set would be stable. 3. How is it when I am trying to bring in a distant station, I pass a certain point on the "volume" dial the music or speech becomes loud and harsh? A.: Your set is oscillating and you must never use it in this condition. Up to a certain point a "volume" condenser strengthens the signal, but_past that point the set commences to oscillate and music and speech become rough. Work just on the other side of this point.

Af M. J. (Auckland).-I have inductively e coupled the loop aerial of my set to an outdoor aerial, which is approximately 80 feet in length, Reception of distant stations has improved 75 per cent,, but I have some trouble in separating 1YA, 2BL, and other stations, Shortening the outdoor aerial does not appear to have any effect, while tuning is no finer by using the large aerial coupled with the loop than when the loop aerial alone is employed. How could I obtain greater selectivity? A.:The trouble appears to be in the set itself, for all loop sets should tune sharply. We presume you have tried the loop at different angles, even though it is coupled with the aerial. If you wish to use a wavetrap, couple it between the aerial and the loop, for the loop is really an enlarged coil of your set.

Novice (Whangarei).-I have a .0005 eondenser and ample 28 and 22 s.w.g d.c.c. wire, How many turns for the aerial, grid, and tickler coil would I need to put on a 3in. former, for a one-valve set? A.: Secondary, 65 turns of: 22 s.w.g. wire. Primary, 22 turns of 28 s.w.g. wire. Tickler (Gif you intend using a .0005 for regeneration), 20 turns, 2. How many plates would I take out of this to make a .00035? A.: Four moving and four fixed.

A.C, -(Morrinsville).-I have logged 25 e stations. Can I expect any others on a one-valve set? A.: Good gracious, no! You have had excellent results-far better than the average one-valye set is capable of. 2.I have connected an extra pair of *phones to my set and find it difficult to tune out the howl. How ean I remedy this? A.: Try the effect of a small condenser across your ’phones-say, .001. If this faiis,

you will have to put in an output filter such as was shown in:‘last week’s diagnosis. 8.1 get better reception without the grid-leak than with it. Why is this? A.:; This happens often because of & faulty grid condenser or grid-leak holder. §.L. (-).-I am building a five-valve .e mneutrodyne, but I cannot follow the diagram, as it is very small. Could you advise me where I could obtain a modern lay-out of this set? :*

A.: There are no modern lay-outs s a five-valve neutrodyne, as this set went put of date about three years ago. However, you will find that we described one, complete with diagrams, on March 15, 1927.

AY DIO. (Eltham).-I have built the "Sparrow Hawk One" and have added two audio stages. The set has a great kick on code, but when I get on to phone stations the carriers are very loud, but the percentage of modulation low and weak, The reaction condenser has a very bad detuning effect, and it is almost impossible to listen to.a distant station. A.: The eapacity of your reaction condenser is rather high, and it would not be a bad plan to use a .0005 fixed condenser in series with the moving arm and earth. You may -then have to increase the numbers of turns on the reaction coil, but generally we think you would get better results. With a differential condenser, detuning is not strongly marked. It is possible you are troubled with a mild form of hand capacity, in which case it would) be advantageous to use a metal panel.

I G.R. (Takaka).-I have a six-valve set, e which has been functioning excellently until recently, when it has become very mushy. What is the remedy for this fault? A.: It is due probably to the voltage of your "C" battery falling off, or the power valve coming to the end of its useful life. Have you checked over your other batteries, just to make quite certain the trouble is not there? Another trouble could be a break-down in the secondary of one of the audio transformers, but this is not very likely. The trouble is most likely a flat "B" battery.

Ic. (Foxton).-Where may I procure the 1929 "Radio Guide’? A.: From most bookstalls. Failing them, you could apply to our office. 2. Which would be the most suitable valve to use in the short-wave adapter deseribed in this year’s "Guide"? The 201A or C509, but 221 is best, A.: They are both exactly the same. 3. What value grid-leak should I use? A.: Por short-wave, about megohms.

OWER TONE (Dunedin).-When the secondary of a power transformer 4 is wound in two separate halves, what lezds» are joined to give a centre tap? A.: Whe end of one and the beginning of the next. These are the two adjacent ends.

Ounsa (Oamaru).-I propose building the "Sellens Short-wave Set." Would a pentode valve be of any advantage in the last stage? A.: Yes, a pentode could be used in the last stage, but unless these valves are specially matched to the following transformer, the results are not always quite satisfactory 2° In the "R.R." you give the diameter of the radio coil and not of the detector coils. | What should this be A.: The same as She radio coil. ' 3. On the broadeast- band, will this set bring in the main New Zealand and Australian stations on the speaker ?-Yes, G.T, (Brooklyn).-I-am troubled by « cross-modulation,: as described in 3 recent issue. Would a wave-trap be of any use? A.: Cross-modulation is very difficult to eradicate, For this reason ‘the multi-mu

Valve Base Coils with .00005 Tuning Condenser and .00015 Regeneration. R.F. Coil. Detector Coil Waveband

}yatve has been brought out. Ag a matter of fact the waye-trap: may possibly do @ little good in that it will sharpen tuning, but the issue is extremely ‘doubtful. 2. Will a band pass filter cure this, and, if so, where should I connect’ it? A.: A band pass filter would certainly reduce the trouble, but it would be more than an amateur’s job to put it in the set. The band pass unit you specify, while being quite satisfactory, would not be of any pee in your set. It would have to be built J.J. (Wanganui)-What is the cor"Ae rection for Daniell cells in issue of Wovember 14? A.: There was no correction in the article dealing with the construction of Daniell cells. A correction appeared for the article on chokes, which followed that on Daniell cells, though we have an idea that the wrong method of adding the sulPhuric acid was given at one stage. Add sulphuric to water. 2. Can I use B442 in the place of B403? A.: You could, hut it is very doubtful if B442 would be an improvement on B405. 3, Would I get better results by increas-ing-my "B" battery to 185 volts and the "C"\ battery 7-9 volts? A.: In all probability, yes. D* 25NC (Picton).-Can any apparatus be added to my set to increase the range for dx work? A.: There is no simple apparatus that ean be added. You could, of course, reconstruct the set along modern lines. 2. Is there a six-volt pentode valve marketed? A.: Yes.. For example, Mullard PM26. P M. (Te Kuiti)-We had two wireless ° sets, working from the same aerial, but once when I switched off one set and turned on the other, something went off in the set, I had just turned off, and I have not been able to work it since. The valves have been tested and they seem all right. What could have oceurred? Is it sate to run two sets in this manner? sy, A.: Yes, it is perfectly safe to run two ygets in this manner, but it is a little diffi. ‘ult to say exactly what happened, It is possible that a leak from your electric set charged the aerial with high tension current which found its way through the aerial coil of the other set to earth. Hxamine this coil and see that it is intact. If this does not reveal the trouble, we are afraid we cannot help you further. I, A.D. (Colac Bay)-I am troubled a ® great deal with a transformer near my residence. Can anything be done? A.: We are afraid, under existing legislation, nothing can be done, You could approach the radio inspector and he could then in turn approach the power board and ask them to rectify the trouble, but that is as far as the law will go. See press matter elsewhere in this issue on that subject. 2. I am also troubled with selecting one station from another, ~

A.: Your make of set is not as selective ag gome, but it can be made fairly sharp by the use of a wavetrap, or a midget condenser in the aerial. We do not happen to know anything about the other set you mention. M° WHARD (Feilding).-In the "Outspan Hive’ there is a condenser between detector and the aerial. I wish to use a similar arrangement to connect the first and second r.f. valves. What value condensers should I use?-A.: The same. 2, I am told that a rheostat and meter are much better than a one _ filament switch. ‘Is it any advantage, and would 10 ohms rheostat be the right value? A,: The rheostat and meter is certainly a refinement, but a switch would do quite

=H well, Ten ohms would be the right value. 8. I intend to put the first two stages of the."Sellens Short Wave Set" in front and connect into the audio stages by means of a D.P.D.T. switch. In this set "A." goes to earth, whereas in the "Outspan" AW." goes to earth. Could either be altered to suit the other? is Alter the "Outspan" to "A..." to earth, Norece (Lower Hutt)-What type of Ferranti transformers should I use in the ac. Radiogram? A.: Kirst audio, AF8 or AI4. Second, and for 171 type power valves O.P.M.LC. 2, What Philips valves are suitable? ’ A.: Philips valves would be quite suitable. Use the following valves :-H428, r.f. stage 1409, detector 415, first audio 1409. Power valve B405. : 3. Where could I obtain the coils ready made? A.: In Wellington you could obtain them from Wear & Co., or the C.A. GNAZ, (Te Kuiti)-I have a five-valve set. Could you suggest a short-wave adapter that I could build and use in it? A.: The best plan wea be Ln use a super-heterodyne type fy) short-wave adapter. Failing either a battery adapter of the "Sparrow Hawk" type deseribed in this year’s "Radio Guide," or the ac. type described in last year’s "Guide." ‘The super-heterodyne adapter was described in the 1931 "Radio Guide." 2, How should I cannect the pick-up to my set, which uses an s.g. detector? A.: Your best plan is to break the gridreturn. That is, the bottom of the grid coil of the detector valve, and put the pickup between the two separated ends. Across these insert a switch so that when it is closed there will be a short cireuit between

the ends. When it is opened the pick-up will be in the circuit. B.C. (Auckland).-Should the d.d.c. e wire, after it has been wound on to the bakelite tubing for the "Knife Edge Rejector,’"’ be left bare or covered with a shellac varnish? A.: It is immaterial. So long as it does not. touch anything else, it is quite in order to leave it bare. 2. Will 50 turns do as well as 47?-Yes. NAD (Tiki Tiki) -What is the best combination of valves for my set? A.: The one you are using, giving preference to the American valves. 2. Would a pentode in the last stage make much difference? A. We are inclined to think not. 38. For best results, what combination would you suggest? A.: The combination you are using is, in our opinion, the best possible. If you are not getting the results you think you should, remember that you are using an allwave set, and this type is always a compromise between short-wave and broadcast. OSSY (Dunedin)-I want to convert ‘my B.D. to an all-electric. Will the following valves do? 226 r.f. det. and first audio, 245 last stage, A.: Yes, but why use 226 in the first stage? Why not use 227, or, better stili, 224? If you want to make an ac. set, why not build the "Radiogram Five" described in the 1981 "Guide"? You need not use a power valve in push-pull in the last stage, unless you are particularly keen on pushpull, The resistances may be, if necessary, by-passed with half m.f.d. condensers. T. (Napier).-Would a lead-in, shield"ed by an armoured cable, affect the distance and volume of signals?-No. 2. Would it be possible to shield, say, 30 eet of a 50-feet aerial, or. is it necessary to do the whole? A.: It would be possible to shield only a portion of it. If the results are not then quite as good as they might be, try shielding the whole. 3. Is there any special procedure when attaching aerial ang lead-in tube ?-No. j= (Wellington).-Which is correct of the two diagrams I enclose? A.: The theoretical, always. Slips are very easily made when drawing the layout diagrams, and in cases of doubt always follow the theoretical.

VOLTAGE (Otago): I have a four-valve kit set, in which there is a continuous whistle which dies down only when the rheostat is turned back. .: Try reversing the connection to the primary of the audio transformer, for we suspect audio instability of some type. When the set was rewired this difficulty should have been overcome. It may be necessary to substitute the impedaformer with a good quality transformer. [uss (Port Chalmers): I have made up & the "Sparrow Hawk One,’ and am puzzled to know why I eannot get 4YA or 2YA. All other stations come in well. A.: There are probably dead spots caused by the aerial at just about these places. Take off a few turns from the aerial coil and, , alternatively, try bringing in the aerial coil to the top of the grid coil, BLECTIVE (Auckland): The selectivity of my set is very poor. What can i do to improve it? A.: The sketches which you enclose are of pieces of apparatus which should help you considerably. With a non-selective set it is a case of having to make an extra

tuning device, which, of course, addg te. the number of turns. A band pass filter’ would do splendidly, and we hope some’ day to be able to describe one, In the meantime go ahead with the second hook-up, and you will find selectivity will be improved. EGHNT (Methven): I enclose a sketth of the filament wiring of my set, Is ‘dt correct 7-Yes. , Beeps 2. At present I have 201A in detector, 5X,’ in the 1st audio, and PN6 in the last sfage. The grid-bias voltage of the PM5X is 8 and on the PM6 7 volts, 120 volts are applied to both stages. The tone through the horn speaker is very harsh. ‘ A.: Your trouble appears to be in the speaker, as your valves are biased correctly. Some of the old horn speakers are very harsh indeed. ’ 8. I have a PM6D valve. If I put it in the detector socket and turn on the set a how! is set up. A.: The valve is microphonie, Try putting a cocoa tin over it, but it is quite probable that this will not stop the trouble. The valve could be used in the first audio socket. It evidently is not suited as a detector, although that type is generally recommended for this place. You are unlucky in striking a bad one.

Aerial, Grid. IT. Anode. Reaction. Metres 34 6 9% 133 204 274 9-12 12-19 19-28 28-40 40-65 80-100 RURERECRERESEDLRSSE LO BERE: