Questions and answers

Radio Record, Volume IV, Issue 38, 3 April 1931, Page 13

Questions and answers

A R.P. (Masterton): I wish to change * the extra long-wave arrangement on my set to short-wave. How is the wiring to be altered? . A.: Had you supplied us with a theoretj¢al diagram we might have been able help you.'§ We are sorry that you have taken so much time to make very careful lay-out diagrams, but we cannot do much to assist you. Possibly you will have to rebuild the radio section, LUND (Westport): I have a five-valve get, and I am desirous of using all possible fixed condensers across the "B" batteries. Where shall I use them? A.: Connect the 1 mfd, condenser between By rt and B-. Also the same eapacity between B-+- detector and B-. ADIO FAN (Wadestown): In your degeription of the Outspan Five you specify three .00035 condensers. As this is hopelessly out of fashion I wish to use a ganged condenser and one separate dial controlling a .0005 condenser. Using 2in. coils, how many turns must « [I use with 24 d.s.c. wire to match these? \ A.: Do not presume that because the Outspan Five was published with three dials it is hopelessly out of fashion and that we brought it out thus knowing full well that we were old-fashioned. We endeavoured to match the coils, but as we explained in the article the task of lining up coils when using reaction is a very difficult one indeed. Yor this reason 80 turns are specified on the second eoil against 75 for the others. Another set we built with redesigned coils necessitated an alteration in the number of detector turns. Very much depends upon the valve and lay-out employed. In your case if you put 100 turns on the -00035 coils and 82 turns on the other eoil, with primaries of 35 in the case of the former and 380 in the case of the latter, with 45 turns reaction, you should be somewhere near the mark, We would like to know if you are success-

ful in getting fullest efficiency out of the two dials. AMBITIOUS (Dunedin) : Where can I obtain apparatus to make a television set? want to pick up the transmission from 8BD and 38UZ. A.: We think you are unwise to attempt to receive television, though if you are very keen write to Hartle and Gray, Auckland, who, wé believe, carry stocks of television apparatus,

CEE Va W. (Dunedin): See last week’s is- * gue, page 30. O W.L. (Greymouth): Your question ° was fairly fully answered by the table in the week before last’s Questions and Answers. K M. (Dunedin): See the R.R, Octo- * ber 3, 1980, or the "Guide," for a full description of the Beverage aerial. (uRIOUS (Timaru) : How can I make a .00025 condenser into a .0 A.: Remove one fixed and one moying plate or switch in series with the eondenser a .002 condenser.

2. Will a shortwave adapter give as good results as a separate three-valve set A.: Not quite; there is usually a choke in the detector circuit that is specially designed for broadcast. 3. Are UX valve bases satisfactory for an adapter ?-Yes. 4, What plate voltage is necessary on the detector?-22$ to 465 . volts. AERIAL (Hokitika) : When the primary connections of my set are round a certain way the set will oscillate only when the condenser is screwed _ right down, but if they are reversed oscillation is difficult to control. A.: Try by-pass condensers between B plus rf. B plus detector and earth. The correct number of primary turns for a 24in. coil to suit your valve is 10 (using 24 dis.c. wire with a .00035 condenser). 2. Tf I use the tickler coil with the set in a stable condition, will the set radiate? ‘A.: Not to any extent. It will not interfere with anyone’s programme. 8. How many turns should there be on a primary coil for split primary neutralisation?-About 25, not slot ‘wound. 4, How can one test for interaction . between coils or grid and plate leads?

A.: It is not at all easy to test for: interaction, You will soon know if it is present because .of uncontrollable oscillation. E A.B. (Hastings): I have a wet "B" * battery. How can I stop leakage round the terminals? A.: By a sealing compound run into the spaces. 2. At present I am using a 32 c.p. lamp for resistance. Would any damage be

done in an attempt to charge the batteries faster if I used a 48 ep. bulb? A.: If you had told us the rating of your lamps in watts as is marked on the lamps themselves instead of in Gp. we should have been more in a position to help you. A B.C. (Waitemata): Is my commer- ® cial set suitable for N.Z. conditions? A.: Unfortunately we do not know anything about it. In all probability it is quite suitable although if fitted with a long wave switch that will be quite useess.

ANCHOR (Matamata) : I can log only 27 stations on my 6-valve all-electric commercial set. What are the reasons? A.: Your set is a first-class one, and unless you have a dud valve your location must be hopelessly bad. Daylight reception is in the best of places very uncertain, but you should get better results at night. Your best plan would be to communicate with the New Zealand ageuts. T R.A. (Wellington): Would the Kes- * trel Three be suitable for shortwave work, as I shall have to use a counterpoise earth? A.: Yes, it should be quite a good re ceiver for the purpose. 2. What outside broadcast stations eould I receive? A.: Having never tried the Kestrel Three under such conditions, we cannot tell you. . 3. What would be the price of the re ceiver to build?-A.: About £6. A M.H. (Tirau): A small wire in my * loudspeaker has twice. broken. Would it be a faulty wire or the vibration of the set? A.: It is due probably to the current. of your last valve passing through the speaker, If you use an output filter the wire should not burn out. ‘

‘2. How can I connect a pair of headphones to my set? ; . A.: If you have the output filter you could connect them at the same points as the speaker. If, however, your set uses push-pull you would need to have the job done by an electrician. 8. I have two pipes about 6ft, in the ground. Would it be better if I used 8 separated by 3 feet? . A.: It is a debatable point. At the present time we are conducting a very interesting examination. According to measurements recently taken there will be no improvement unless the pipes are separated by 6ft., but many readers state definitely that their reception has beeen improved by the installation of such an earth, 4, There are three wires from the set, but only two go to the power point. the third for an extra earth? A.: It is an earth connection "to be used with a three-point wiring system. yor (Kurow): We cannot iell you much about your adapter unless you tell us the name of it. It appears to be a commercial set and we are somewhat in the dark. BRAtCUP (Wellington): I wish to fit a remote volume control, but am deterred by the necessity of extending the three leads of a potentiometer. A.: Your best plan is to use a variable resistance of about 500,000 ohms across the aerial and earth terminals, This is quite a satisfactory means of con trolling volume. How can I overcome the motor-boat-ing when the detector is followed by an r.¢c.c, unit? A.: It is due to the resistanee in the grid circuit not matching the valve ov.

QWING to the increasingly large number of queries that our Technical Department is called upon to answer, we have found it necessary to make some slight alterations in our system. Commencing with our issue dated April 10, each correspondent will be restricted to three questions. Those who wish to have more questions answered, or who desire a reply through the post, must enclose stamps or postal note to the value of 1/We regret that this has been necessary, but to a large extent it has been brought upon by some correspondents "overstepping the mark." Letters containing from 12 to 20 queries are not uncommon, and many of these could have been answered had the correspondent looked up either back numbers of the "Radio Record" or the "Radio Guide." Here are some interesting facts concerning the numbers of queries we ‘have handled during the last six months: There have been approximately 1,500 letters, representing 5,000 to 10,000 questions, This entails a great deal of work, but where we are helping a correspondent genuinely in difficulty we are pleased to be able to do it. =F, oe eee eee

_ ORRESPONDENTS 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 ...-scoecoocecccc0c0e® Number of valves .occoceseessoc0000e Name Address eeeocec oso acs0OSOQ0B30O90G08 086 00000000000900 000080008 0009008 00080000 000 900YTOSOGOOSOOD HOB 006000500 0000000000 000880008 000800800F Nom de plume 0000080008 000008008 To be kept in subsequent inquiries. Date Seeeoenseneese eeeervocoscve Please Note:(1) Be specific and brief, tabulating, if possible. (2) Write legibly, and on one side rt) e paper. (3) We do not design circuits, but accept suggestions 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.

‘the condenser being of the wrong value. 4Phe seorrect values. are as Plate -wesistance, 100,000 ohms; grid-leak, 1 meg, .Coupling "condenser should be from 001 to .6 mfds. High voltage should. be applied to the plate resistance, say. from .*5 to 130. volts. B. Aled switching over from gramophone reception the radio signals take from two to three minutes. to ecome through. A.: This sounds very much like a defective switch. Prize the prongs together and clean it with sandpaper. 4, The switching on and off of a house light effectively cuts off signals for a "period of from 15 to 80 seconas. Signals then come in again gradually. A.: This may be due to a fault anywhere in the receiver, and it will be ‘very difficult to locate without tampering with the receiver itselt. It may be in that r.¢c¢. unit. 5. How’ can I reduce my detector volt- : oze. below 100? : If you are using r.c.c amplification ‘it hot necessary to "reduce the detector voltage any lower, but for transformer coupling a fixed resistance of from 10,000 to 15,000 ohms would reduce the detector voltage to a suitable figure.

FE. J. (Ohura): Also see full acount of the Beverage aerial published in the "Radio Record" of October 3. F, L.R. (Chch.): Regarding the Night Hawk Two, the signals are unaltered whether or not a grid-leak is used. en is accompanied by a back lash. : Try connecting the 400 ohms poacross your "A" supply and taking the variable tap to the grid-leak. This of course is not connected in parallel across the condenser as is shown, but is taken to the gride side of the variable tap. The grid return is then taken to A-. PUZZLED (Gisborne) : I recently built a booster which failed to’ give -good results. A.: We are not really surprised at that. Our experience with boosters has been that very few work satisfactorily, and we do not recommend their construction. If you want to incorporate a s.g. valve you

should rebuiid the radio section of your set and use the improved method of trans- ° former or tuned .anode coupling. 2. Can I couple the grid leak and the grid condenser in series? A.: No; if you are attempting resistance capacity coupling you are quite wrong. We publish a diagram showing the correct method of coupling valves by this system. DIEHARD (Seddonville): Will you . give me particulars of the Daniell Cell and will it keep my five-valve American battery set charged? : The charger was descibed in detail our issue of November 7, 1980. It would not, however, be suitable for your set, as the total filament consumption would be well over an amp and the rate of charge with a Daniell Cell is only about $ an amp. M.D. (Blenheim): What valves * would give the best results in my American sets. The present are 201A’s, but I want to use Philips or Mullard. A.: For best results you should use the 201A’s or the newer valye, the 221, in the radio stages. For detector you could use A615 Philips or P.M.6D Mullard. On the audio side you could use A609 Philips or 5X Mullard. For the power valve Philips 605, Mullard P.M.6. BG605 has an output. of a quarter of a watt, 2. Can a pentode be used? A.: Yes, merely by connecting the auxiliary grid to B+ 8. Is the enclosed arrangement of "CO" batteries correct? I find I have to reduce slightly from the approved ratings. A.: For the first audio stage you need only 8 volts, and for the last stage it is sometimes necessary to depart slightly from the manufacturers’ specifications. 4, What type of volume control. is on my set? What type and size would be hoes to replace the one that has burnt om We do not know. If you took your set ‘to a reliable dealer he could tell you the resistance of the volume control and replace it for you. 5. Does .a Daniell Cell charger need an external source of electricity ? : No.. The Daniell Cell as described in the "Radio Record" of November 7, 1930, points out that it generates a supply of electricity which can be employed

for battery charging or even for operating a set directly.’ 6. Beside the long lead, is the aerial of which I enclose the plan good? A.: It is pretty, and we consider you would be better with a single aerial 40 feet high and with a short lead-in. One aerial tends to screen the other as you now have them, 7. Is a brief description of the Pierce earth system possible? .: The Pierce system was described in the "Radio Record," March.6, 1931. QUEST (Cheh.): I have built an Ndison element battery. Where could I obtain particulars of a home-made charger? A.: The 1930 "Radio Guide," of which copies are now difficult to obtain. This will suit your purposes, 2. Could I charge the whole 90 at tery or would I have to split the bat- : You could charge the whole 90.

3. How long should a charge last, using my set six hours a day? A.: That depénds upon the capacity of your battery, which. we do not know. 4, What are the best valves to use? A.: Five 201A’s or 221’s, or their equivalents, and a 171 type power valve in the last stage. This must be suitably biased.

QUERY (Te Awamutu): For results. which short-wave adapter is the better, the one described in last year’s "Guide’’ or the one described in the 1931 "Guide’’? A.: The superhet. adapter in the 1931 "Guide." 2. I have heard that hum is inclined to be objectionable. A.: You will always have to face that with a.c. shortwave reception.. However, a special article has been devoted to a shortwave power pack which describes very fully all the smoothing necessary for that type of eliminator, and this should help you in eliminating hum from the super het. power supply. G L (Auckland): My aerial is 100ft. long, double wire. Will a variable condenser in series with it increasé the selectivity ?-Yes. 2. What set not exceeding five valves is the best for volume on distant stations and: tone on the local station? .: "The Radiogram Five," in the "Radio Guide." 3. For the Two R.F. B.D. which is the better ratio for ‘transformers, 34-1 or au

4-12?--A.: There is really very little dif | ference between the two. 4, Which are the best valves for the 2RE.B.D.? . A.: Valves of the 201A type in the radio stages, a detector of the 615 or 6D type; audio valves, again the 201A type and for a power valve the 605 type. 5. Is unspaced d.s.c. wire as effective as spaced enamelled wire? A.: That very much depends upon the shape of the coil and the total number of turns to be wound on, The best plan is to follow the directions given and not try to make any adaptations. All coils are very carefully worked out before they are published. . 6. What is the best metal for A.: Hither copper or aluminium. The former is easier to work but the latter more effective. KEVO (Invercargill) : My set will not operate below 212 metres, althoug I ean tune down to represent 200m, A: though I can hear stations down here I cannot separate them, A.: We cannot tell; it may be anything. Perhaps your coils are not matching when you get up on to those very high frequencies. It is a case either for a serviceman or-to be ignored. 2. How ean [I reduce hum in my a.e. set? A.: You cannot, unless the set is home made. Hum reduction is a matter for a skilled. engineer. Buppy (Masterton) : What solution is used in a balkite battery charger? A.: 1.200 specifie gravity H2S04, This can be obtained from any battery service YCLOTS (Wellington): I am constructing a 1-valye set the cireuit of which is enclosed. When I disconnected the "B" battery I could still hear music. — A.: That is not altogether unusual, as’ your valve is still operating because of the effective of the "A" battery on the plate.

ANS. (Dunedin): How can I make my crystal set more selective? .: By using a variable condenser in series with the aerial or by rewinding the coil using the circuit that was described in this year’s "Guide." 2. How many turns of the enclosed Ww ire must I put on a 2}in. ebonite former? A.: It ‘is 18 dee. You will need 80 turns. . 8. Can you suggest anything that would improve the set? A.: It is very hard to get the circuit of your set from the plan you have sent along. Apparently, however, you are getting good results and alterations would not be ‘worth while. Ts MIRO (Cambridge) : Should the firs\ valve of my set be discoloured as with smoke? . A.: This is probably quite in order. The chances are very much against anything being wrong. 2. Am I using the correct valves? A.: Your power valve could well be substituted by B405. The 120 valve is a three volt power valve, whereas your other valves are four volters.

| 3. When I put my finger on the frame work the tone becomes deejier and clearer. Should this be? ae ‘ A.: No; try connecting-the earth where you place your finger, and if the result is the same leave the earth in some way connected to the metal.cabinet. If not it would be advisable to get someone ‘to have a look at your set. R B.G. (Auckland): I am troubled * with heterodyne interference with 2YA. It is due to the local station, which, however, operates on a frequency very much removed from 2YA. I rePorted the interference, and have received & reply that it has not been noticed elsewhere, A.: Apparently your trouble is due either to a fault in the screen-grid valve or to a reflected frequency. A wavetrap tuned to the interfering station’s Wavelength would probably be effective, and you should try altering the direction of your aerial. Try another valve in tHe s.g. socket, X. (Dunedin): Can an audio trans- * former with a burnt-out secondary be put to any use? A.: It can be employed as part of- . 4n output filter when a small power valve is used in the last stage. It ean be used as an audio-frequency choke elsewhere in the set under similar conditions, 2. Can the enclosed circuit be improved? A.: It is unusual not to have the screening grid by-passed to earth; in other words, you should have a .5 mfd. condenser between B+. 67.5 and earth. It is unusual, too, for the s.g., working as detector, to be followed by transformer coupling, R.0.C. is the more usual. However, you have been getting good results, ahd that is everything, | EK J.C. (Marton): My set distorts X * badly, As? See "Distortion" in the "Radio \Guide," as it may be due to a large number of causes. The correct voltage for the output yalve PM2 is 12 with 150 on the plate. For other voltages ‘the bias is proportional. 2. I have the eliminator in close proximity to the s.g. valve with no shield between. Would this affeet reception? A,: It will probably cause instability, The s.g. valve should- be. shielded from the power supply. . There are several small stations that I would like to get. Is there a list, with addresses, in the "Guide"? A.: Yes, the full addresses are given of all Australian and New Zealand broadeast stations, while adequate addresses are given for the American stations, 4. Several people in thiy locality are troubled with a bad power leak. To where can I make complaint? A.: The District Radio Inspector, WelJington, ; {, 5. What value of condenser is required ror the wavetrap described in the "R.R." of March 6-A.: .0005. ' 6. 22 and 18 gauge d.c.c. wire is. given. What gauge s.w.g. would this be? A.: D.c.e. is, so to speak, a species of S.w.g. wire. D.eec. relates to the covering meaning double cotton covered, so that by 18 gauge d.c.c, we really mean 18 standard wire gauge double cottoncovered wire, but you see d.c.c. is ever so much shorter, H C. (Waimate): I have the core of * a toy transformer Can I use it to supply filament voltages for all types of valves? A.: The laminations are fairly small for the job they are called upon to do, and it is doubtful if the window would take all the winding. However, here are La the particulars. The primary would need 4 to be 2000 turns of No. 30 gauge wire; for the secondaries you can compute the number of turns at 11 turns per volt. The gauge wire you use for the seconwill depend upon the amount of current you wish to draw from the transformer. ou could not take much

HGINNDR (Dunedin): In my all-. wave set I am using PM2DX, one Lf. and B205. . Is this a good tion ?-Yes. 2. Do I have a good set?-Yes. 3. I have a 2 x 2 accumulator each 60 amp. hours. Using the set for 4 hours a day, how long should the charge last? -A month. 4. I am using a "B" eliminator. What fixed resistances and condensers do I need? A.: See any of the last three "Radio Guides." 5. Would an electrolytic condenser be better than mica condensers?-yYes, if it is of the correct capacity, say, 16 mfds. 6. Will I destroy headphones when using a "B" eliminator? A.: No, but if your last valve passes a fairly large current you should use an output filter. 7. What is the correct way to put earphone cord clips into the plug?

A.: You must trace out your jack clips and see what goes to positive. 8. On shortwave oscillation is ploppy. How can I alter this? A,: By trying different grid-leaks and if necessary a different grid condenser. Alter the detector voltages, trying different valves, if necessary bringing the grid return to a variable point between positive and negative, as‘shown in the "Diff. Four." 9. What is the best value condenser to use in (a) shortwave sets, (b) all-wave sets? A.: Shortwave .0001 or .00015; (b) .00085. Use the switching arrangement shown herewith to reduce the effective capacity. ‘ 10. Is a .00005 condenser quite suitable for reaction?-No, it is too small. 11. Should I use a different grid leak for broadcast and shortwave? A.: Yes, broadcast 2 megs., shortwave 10 megs. 12. Can reaction be used satisfactorily with a power detector ?-Yes. 18. How long should my aerial be?Total 100 feet. 14. What is the proper value of resistance to bias suitably a 2247?-4000 ohms. 15. Would a Bluespot 66R unit he quite O.K. with my valves?-Yes. 16. What gauge wire should be used for aerial and earth?-7/22. 17. Why should I get 2YA in two places 14 ‘deg. apart? A.: It is due probably to an effect set up by your set oscillating. Ti (Havelock): For some time I kept my set stored in a dry place, and when I turned it on, although the valves lit, I could not get ‘anything through for about three hours, and then Wellington came through weakly. When I put the voltage up from 90 to 135 and the "CO" battery to 9 volts the tone and volume dropped. A.: Although difficult to define the cause of a trouble so unusual, we would imagine that although you tested the batteries they are at fault. Test both "A" and "B" batteries again after the set has been operating a while. Batteries must be tested on load to determine their efficiency otherwise without seeing the set we cannot offer any solution.

J ACK (Wellington): Is a filter affected by the placement of the smoothing condensers in relation to the ‘¢hoke? : A.: Yes; a condenser should be on ‘either side, and not both on the one side. NOvich (Christchurch): My set uses 6-201A valves. . Should it have a power valve in the last stage? A.: It most certainly should have a power valve in the last stage. One of the 172A type is quite suitable. It must, of course, be adequately biased. 2. How can I tell the last stage? A.: The last stage is the one that is nearest the speaker. Trace the plate lead of the last valve socket, and you will see that it goes to one of the speaker terminals and not to a transformer or resistance, 8. Which speaker. is the most suitable, horn or cone?-Cone, . 4, What is the difference between a& neutrodyne and a heterodyne set? A.: It is a long story and has been told in full, with illustrations, in the 1931 "Guide." Both sets work on an entirely different principle up to the detector stage, when they are alike. It is really a repetition of the broadcast station itself, within the set, only the radiations are not allowed to go on to the aerial. 5. What stations should I be able to receive? A.: That depends upon your locality. You should be able to get the Australians quite satisfactorily. 6. Hxplain the Beverage aerial. A.: See the "Radio Record" for October 3, 1930. Q R.M. (Waikato): The generator of * a nearby picture plant has been causing interference with my set. Can it be stopped? A.: Yes, it should not be allowed to cause interference. If you cannot get satisfaction with the management, write the District Radio Inspector, Auckland. Do not, however, incorporate the paragraph referred to in your second paragraph.

PORTABLE (Wegtn.): We have not tested the apparatus to which -you refer, but we suspect it would be more expensive to operate than a.c. apparatus. 2. Would it be possible to use an Addaphone with this?-Yes. . E N. (Napier): Who are the agents for * Pilot super watt? A.: Harrington Ltd. Willis Street, Wellington. 2. What is the cost without the eabinet? A.: It is sold as a kit set with a gmail eabinet for about £27. 8. What sort of a set is it ag far as strength ‘goes? ' A.: We have not tested it. H N.S. (Waihi): What would be the * eost of converting my factory-made set with honeycomb coils to the Outspan Five? At the present time I am using five 201A valves. A.: We do not know how much it would cost, as it would all depend upon the number of parts from your old set that could be used. You would certainly have to have a new set of coils, which, however, are not expensive. How long should my 100 amp. hr. battery last without being charged? A.: About 50 or 60 hours. ; 3. How long should the "B" batteries ast?. A.: This depends upon the drain of your set and the type of battery used. We have given a very complete table in the "Radio Guide," together with explanatory matter which should interest you. Based upon two to four hours’ service daily, a super battery should last you about 10 months. 4, Would the Daniell set chirger be suitable to charge my set? A.: No, it is intended only for sets with a small "A" current. X x4 (Auckland): Can you tell me if "and how a battery s.g. set can be converted into an all-electric to be used from the direct supply? (Concluded on page 30.)