QUESTIONS AND ANSWERS

Radio Record, Volume V, Issue 21, 4 December 1931, Page 14

QUESTIONS AND ANSWERS

FRANK

KEE

The Technical Editor wiil, through these columns, be pleased to help readers experiencing trouble with their sets, Queries are limited to three-for more than this a shilling fee is charged, and a similar fee is payable for queries answered by post. Supplying layouts. circuits and solutions of intricate theoretical. problems is beyond the scope of this service. . A coupon must accompany all requests for information. Nonappearance of the coupon in any issue eannot be regarded as a reason for its not being used. Address all queries, The Technical Editor, Box 1032, Wellington.

pro (Wellington): My commercial set is not as selective as it should "be. I live about 500 yards in a direct line from 2YA, my aerial being 100 feet "Jong and. 35 feet high, and at right angles "to 2¥YA. Would the use of a wavetrap ,or the shortening of my aerial better "conditions?

A.: The use of a wavetrap would probably be quite effective. Shortening your aerial would also reduce the pickup from 2YA, 2. Is Oriental Bay a bad locality as far as distance-getting is concerned? A.:-We have not heard of any good

logs being put up in that district. Propably 2YA is overpowing them. 3. Is there any remedy for static noises, ‘Which trouble me a great deal even on the New Zealand ‘stations? A. Statie cannot be reduced. It is not unlikely, however, that your trouble is due to power interference, ‘This ean be overcome satisfactorily only with the close co-operation of the P. and 'T. Department ‘and the Power Board. ° AUpIO (Wellington): I can separate the two local stations by using a selective. crystal set, but although there is a space between them one can be heard in the background of the other. A.: This is due to a form of cross-modu-lation which is very difficult to eliminate. 2. I am thinking of making up a two or three-valve set to be a top-notcher on the local stations. What do you consider would suit me? A.: The "Multi-mu Three," which we shall describe in the "R.R." shortly. prxew (Wellington) : When replacing valve, does one have to use the same make? ; A.: No, so long as you use the same type, the change will be satisfactory 2. Which is the best earth wire-bare or heavily insulated? A.: It is immaterial. There is no need to haye the wire insulated, 8. Your yalves are in the right place. You could not transpose a 610 and the 227 because of the difference in the bases. ONDERING (Christchurch: How can I improve ‘my aerial? Since getting a new set I have been picking up more noise than formerly, and I think the aerial must be at fault. A.: The aerial is not at fault. The fact is that you are using a sensitive set in close proximity to leaking power lines. and you will always get trouble like that. Your aerial should be at right-angles to the light lines for best results, and leadin should be of armoured flex, with the armouring earthed to a zround connec. tion distinet from your set earth. Often shortening the aerial or using a condenser of .0002 (approximately), in series with the aerial, will. have a marked effect in clearing up noise. ERIAL (Auckland): My aerial is about 30 feet high at the far end, and 20 feet at the near end. It passes over a hedge eight feet high. Would this affect it in any way? . A.: Yes, passing over a hedge diminishes the effective height. It would be advisable to erect your poles 20 feet higher if possible. We do not know ‘anything about your set, but it should be capable of reasonably good performance. We do not know how you could improve your results other than by improving your aerial as we havé snegested, looking to the earth, haying the valves tested. and the condensers lined ay. Dxs6 (Christchurch) : Three valves of my six-valve battery set are controlled by a rheostat. The others are connect:

ed directly with the "A" supply through a resistance. Will this harm the valves as I am using 5 201A’s and A609 as detector. . "fo. . A.: The valves will not be harmed. A better valve combination would be 221's in place of the 201A’s except in the last stage, that is, the one nearest the loudspeaker. In this socket you could use a medium power valve of the. B605 class. A609 can still be used as detector. 2. What type of "B" eliminator would be satisfactory for my set? .: You will require ‘one delivering 180 volts, 25 to 30 mamps. TONY (Auckland): I have constructed the Radiogram Five, . with two stages of r.f.. but sensitivity is poor. I have tested the wiring and the valves. Could I effect any improvement by altering the number of turns on the primary?’ In all probability, yes. Inerease, the number of turns until r.f. instability makes the addition of further turns in possible. Try reyersing the connections tv the primaries. Bring your aerial to the grid of the second r.f. valve and test from there onward. By this means you will probably locate the trouble. Dw: Sorry we cannot answer your first question, but we are getting pretty tired of questions involving coil design. Literally dozens of combinations at one time or another have been published in either the "Radio Record" or "Guide," and among these you should find what vou want. The specifications for the differential. series are fairly near the mark. See "Questions and Answers in Radio." 2. I propose to charge "B" batteries from a tunga charger delivery 2 ampls, I can connect the batteries: in’ blocks of 8 volts. How should I set about making the charging rate suitable? .: You do not state the total nini%yr of "B" cells to be charged. , The propér method would be to charge in blocks’ of 20. Aik SPRITE (N.P.): 1 intend building a super. het. short-wave adapter for my super het. set. Is the valve I indicate the one to connect it to? A.: As far as we know. yes. You must connect the adaptor to the pin which stands by itself, You cannot do any harm by not connecting to the wrong pin. Novice (Eltham): See the table of short-wave calls published in the "Radio Record" on April 152 ~Number 3 will be about right for your purpose. NOVICE (Otago: You may have difficulty in getting the de Forest 442. You could, however, use any other reputable make of the same type. :-Instead of the 201A and 609 use 221’s,: gr their, equivalents. B605 would bea ‘vety suit/ able valve for the last stage. * © A B.C. (Green Island): "We do not * know where you can obtain a circuit of your set unless it is from the agent who sold it to you. Instead of the

— I12As yould could use B605s, which are lighter on "A" -current. We cannot un.derstand how .four valves are used in push-pull, and for this reason it may be better if you could get someone who knewa little about radio) to examine the set and. see if changés could be made. Probably they could. Probably you would have difficulty in obtaining an "A" eliminator to deliver sufficient current. Generaly speaking, a wet battery and a charger are better. It very rarely hapfens that in adjusting the valves any radical change has to be made to the eircuit of the set.: . D*NAMO (Waitomo Caves: Which "would be the better adapter to use with my Outspan Five, the superhet. described last year or the first two valves of the Sellens Short-wave Set? A.: The latter would be preferable, as) you do not have ‘sufficient amplification to work a superhet. satisfactorily. 2. How would I change the Outspan Five so that ‘‘A--" is earthed? A.: Break the connection between the primary and secondary of the "Outspan Five." Connect "B-’ with "A-+-" and connect the two to ground, Take the grid return.of the second r.f. valve to the "A" filament return of the detectox, and two audio valves to "A-". 8. How does one arrive at the number of turns and size of wire for the primary windings of coils, as I intend to use 3in. coils for the secondaries? A.: We think you are unwise using 3in. eoils for the secondaries of the "Outspan Five," if that is what you mean. For broadeast nurposes the ordinary primary varies with the valve preceding it, but as the calculation of the number of turns involves many factors that are likely to get the amateur into deep water, the best. plan is to take one-third of the number of turns on the secondary and then adjust until the ‘best. results are obtained. For short-wave you can find our the number of turns by comparing the coils you intend to make with some already made, even if the size is different. ' GIMPLHX (Waikanae): We eannot \? suggest anything else without seeing your set, Probably you are making some simple mistake which cannot be rectified by correspondence. We cannot get any line on to your trouble other than what we suggested in our previous answer.

As far as a set is concerned, we would suggest a detector and two audio. There would be two dials, one for tuning and the other for regeneration. You would need a third control-a rheostat switch, but we do not know whether you could get the circuit you require; and if you eannot locate one, write to us and we shall send you one. We can only undertake, however, to send you the bare circuit with an idea of the layout. CABNS (Auckland): My aerial is 30 ' feet high and 70 feet long, including the lead-in. Could this aerial be improved by turning it into a double wire one? A.: In all probability, -yes, Separate the wires by hard wood spacers and keep them six feet.apart. 2. When replacing your valves use one well-known make only. You need four type-24 valves, two type-45, and one type-80. 3. What effect has a copper ball soldered on a short aerial? A.: Very little; we do not advise the use of patent aerials. C D. (Katikati): My aerial is 37 feet * high, passes over my house, eight feet higher than the roof. Does this affect reception and cause noises and attract static? My neighbours have comparatively little. . A.: No, The effect of the roof should be to diminish noises and signal strength, certainly not to increase them. The noises may be due to a power leak nearby, or it may be due to something in your set. Take off the aerial and note the effect. If the noise persists, then there is somethiing wrong within your set. If not, we are afraid you have either a power leak nearby or there is a loose connection 3 the aerial, It may be shorting with the ground, Your aerial should run at right angles to a power line, not parallel with it. QGHORTWAVE (Temuka): I have constructed special s.w. coils for the Cossor Melody Maker and get good results on all except those below 30 metres, although on this band oscillation will take place quite readily. Why is this? A.: Probably because your aerial is too long and you cannot tune below its norma] wavelength. Try the effect of a midget condenser in series with the aerial. 2. I have shifted the rheostat control of the screen circuit, and placed it so that the control applies to all the filaments. I find this better. A.: For shortwave it is generally better to have the filament control in the detector circuit, for that valve is very eritical on the high frequencies.

L P.H. (Dunedin): To further improve ¢ your earth try the multiple system, separating the units by several feet. Bring the leads together and take them into your set in a cable. However, it is possible thac this is not the cause of the insensitivity. We do not know a great deal about your set, but believe it to be quite good. We would suggest that you balance up or have balanced up the condensers, and have your valves tested, D* (Dunedin) : As far as we can ascertain your condenser is a .0001, Coil particulars were given in the "R.R." dat: ed April 2, 19381. To make your con: denser into a .00015, you will require about three or four extra plates. To reduce it to .00005 you should leave two fixed and one -moying, although, with plates so large as this, the condenser may not be satisfactory. Usually for very smal] capacities, midgets are used.

ene R. G. (Karoro): For the "Night Hawk Two" I have a coil consisting of a secondary of 88 turns, tickler 23, and primary 8. It oscillates quite well, but the stations are -weak on phones. If I add to ‘the tickler the set squeals badly. By adding to the primary, signals fade away and oscillation is patchy, Pe dia at the -bottom and top of dial A.: Probably your choke is at fault. You ‘should be able to put more turns on the primary. The correct number is between 20 and 30. This would cause the weakness. ‘Try another choke and then add more turns on the primary, and we think you will surmount your trouble. Are you quite certain you are not using an aerial which is too long? About 120-130ft. is about the most you should have. A midget condenser in the aerial will often shift dead spots, though the proper way is to adjust_the number of turns on the primary. Your broadeast coil is of the right spesification for the broadeast band. TPHIRD GRID (Greymouth): How do the regulations concerning radio servicemen affect the amateur transmitter? Can. they construct and use their own apparatus without passing the R.S. examination? Can the ordinary enthusiast construct his own apparatus where it is operated from batteries. A.: The radio serviceman’s examination prevents anyone without the certificate from interfering with any apparatus that can be connected directly with the mains. Hven although you are an amateur transmitter you do not have a license to construct mains apparatus. Apparatus should be made and installed by licensed radio servicemen or licensed wiremen, ‘There is nothing to prevent you constructing any other apparatus, however. 2. I wish to make a broadcast coil on a valve base extension without either increasing the diameter or making the coil too long. Can I get over this by winding the layers on top of one another? A.: No; that is not an efficient way to make a coil. The best plan is to use very much finer wire than usual. You could calculate the number of turns and gauge of wire from the tables given in the "Radio Guide." 8. As putting valves in parallel halves the impedance, could a high actual gain

per stage be obtained by putting two high: type valves.in parallel A.: The idea is feasible. Of course; there is the expense dnd you may have some difficulty with neutralisation. How. ever, it would be an interesting line to experiment along. M. (Auckland): Your connection¢ * gre not quite correct. You should. wind a separate coil on the high potential end of the secondary of your de, tector valve stage. This should be about 25 to 80 turns "of No. 26-30 wire, The lower end is connected to the plate of the valve. The other end is connected to the by-pass condenser and the top of the transformer. A. variable con-. denser of a capacity of .00025 should be connected’ to the top of the audio trans former; that is the point already referred to, and the moving set of plates to earth., You will be then able to control reaction. quite satisfactorily. You may have to. take the fixed condenser out of the citcuit, ‘ IGARO (Glen Hden)-Would 18gauge single cotton and enamelcovered wire do for chokes deseribed in the "Radio Record"? If so, how much wire would be required? A.: It would do quite well, and you would need slightly more wire than 'you would for the d.c.c., because more ecules be wound in the space provided. more you can get in ‘there the higher the inductance, and the better the smoothing properties of the choke. We suggest ‘that you buy 14Ib. 2. It would be as well to try the condenser on either 'side of the choke to see which way it functions the better. We note with interest your comments. regarding the "‘Guide." (COUNTRY (Frankton).-TI wish to ‘construct.a small shortwave set.. Should I make a one-valver or an adapter of the aame ‘circuit? : We suggest you 'make the adapter, can then use that as a one-valye set, or it can be connected with the’audio system of your existing five-valver. 2. Would a rheostat be necessary? If Su. Where should I use it? : Connect it to the filament circuit. It Aer ala take the place 'of a filament switch. . . 8. If of any advantage, give of an aerial tuner for a shortwave set. A.: It is doubtful if an aerial tuner would be of much use in a shortwaver. Jt may interfere with the oscillation of your set.