Questions and answers

Radio Record, Volume IV, Issue 10, 19 September 1930, Page 24

Questions and answers

MT OVICH (Dunedin). -Would two wires 70 feet long and 30 feet high be better for an aerial the same height and length? A.: Yes, providing the wires were at least 6 feet apart, and separated by nonconducting spacers. K V.W. (Dunedin).-How many turns "™** would be required on a two-inch former using 00035 condensers for the aerial and secondary coil of the Brown-ing-Drake described in this year’s "Guide"? . A.: You will not need an aerial coil for fthe B.D, if you use the usual circuit. The aerial coil is really a taped secondary coil. For this and the secondary of the x.f. transformer you will require 77 turns of 24 d.s.c. wire. 2. Where shall I tap the aerial coil?

A.: At about the twenty-third or twenty-fourth turn. 3. Where will I tap the secondary coil? ‘-A.: As we have explained, aerial and secondary are not both used for the B-D. 4, Can I use 80-gauge d.s.c. wire for primary and tickler? Yes, 5 How many turns will I require on the primary to match A409? A.: 18 turns.. J H. (Wellington).-Can you help me in * tuning in outside stations? Where would I expect to find some of the Sydney stations? I give the readings of several of those already received. A.: It would be a long and a difficult task to give you the approximate readings for each of the three dials. They are very nearly matched, and you should get some of the other stations quite easily by

comparing their frequencies with the frequencies and the dial readings of those you already have. You could make a graph for yourself such as was used to illustrate the response of the Atwater-

a eee eee ae = Kent receiver reported on in our issue of January 4, 1930 W L. (Napier).-I am troubled with *a.c. hum, and am using an eliminator and grid bias unit. This seems to be picked up from the power transformers by the first audio transformer. A.: You must completely shield one from the other by an iron screen which should be earthed. Introduce a little more capacity in the grid bias unit by shunting a two m.f.d. condenser between the terminal and earth. 2. The set is inclined to get out of control¢if worked by an inexperienced person. If the compensator is turned too far, the set will oscillate. There appear to be no grid condensers in the radio circuit. A.: Probably neutralisation is carried out by grid suppressors, and these are evidently cut down to a minimum, so that when the set is forced, it bursts into oscillation. 8. Does a 200 A valve distort due to its high amplification factor? A.: Not if it is worked in circuit, the grid return of which is negative. 4, The set tunes rather broadly, and the locals have double setting, usually some ten metres different. Is my aerial too long? A.: The double setting on locals is due probably to overloading. There comes a point when your set can handle no more and if forced past this point the signals become much weaker and appear stronger when the point is passed. It may be due to reflection though this is unlikely, If you are using a series condenser in your aerial, it is probably not that which is causing the trouble. yp DOUBT (Lower Hutt)-What is j } } ] ] 1 : : : j : 7 : 7 7 : the meaning of the two sets of speci- | fications for tuning coils in R. the W. Three? A.: The smaller numbers are the regeneration coils. What is the correct combination of, areily Philips, and secondly, Star valves? .: Philips for quality, det. 615, audio 609, second audio 605. For sensitivity

use 609 biassed by 4% to 9-volt accordingly to the plate voltage in the last stage. Star valves are probably American type, and you would use three 201A’s.ACE (Kakahi) : I am using a tor-valve regenerative set which has the habit of into oscillation which, cannot be prevented until the dials are moved. A.: Have you tried reducing the detector voltage, substituting the grid condenser and grid leak and reversing the connections to the tickler. It may be due to lay-out of the set. The one used in the 1980 "Guide" is probably the best for the h.r. receiver. NOVICE (Auckland): I have bought a trickle charger, but there are no instructions. I have a two-volt accumulator and want to know something about charging. A.: If we remember rightly there are four terminals on this charger. One is marked-and the one nearest to this is for two volts. If it is not marked you must take this one and the negative for your vurposes. The negative is connected to the — terminal of the battery and the -+- to the + terminal. Keep the accumula-

ISTENERS 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 wcccoesssscvcsevvosecee Number of Valves cessesscceceseces Name se eveeccererereccecasscsones AdGreSS cesccccccccecesecccccosers Nom de plume ..cececcrccccecececess To be kept in subsequent inquiries. Date cerevescsvvecererersecesoseres Please Note:(1) Be specific and brief, tabulating, if possible. (2) Write legibly, and on 92g side of the paper. a (3) We ado not design «.Q°WAits, but accept suggestions ‘or 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.

4 ss WovLtp correspondents refrain from using the noms ‘de plume, "Novice," "Puzzled," "Reader," or "Subscriber." A record is kept of each inquiry, and when many correspondents use the same nom de plume, matters become complicated. Rather use initials. There are still a few not using the coupon. a oe ee ge ge oe ee, ge es oe ee a en

— tor charging until it bubbles, or if you have an hydrometer, until it is registering full strength. It is difficult to estiate the length of time to charge a batjudging from the number of hours set is used. Te, I improve on the valve combination by using a pentode? A.: A pentode may strengthen up reception quite perceptibly, but the combination you have is a safe one. hat grid bias do the above valves poguire? I am using 120 volts B. .: PM2 at 120 volts requires 7.5 volts. : 4, What is the most economical way to provide it? I use an eliminator with 180 volts, A.: It could be taken from the eliminator, but for such a small quantity it is not worth while. By taking it from the eliminator you stand a chance of introducing hum. 5. The instructions say when using an eliminator a potentiometer must be used for regulating the potential on the s.g. valvé. What does this mean? 5. Tf the taps on your eliminator are not vdriable a resistance should be connected in the lead to the screen and varied so that the best results are obtained. 6. Which would be the better earth, one going out the window 10 feet long, or one to a. water pipe 15 feet long?-The former. WINDARA (Dunedin): Can I use a 1 .00035 condenser with 70 turns of 24 gauge wire on a 3in. former for a _wave-trap ?-Yes. i 2. How would a triangular aerial funcon A.: It would be no better than ordinary: L type. 8. Will the lead-in running parallel in‘side the house have a counter effect on reception ?7-No. L G. (Taupiri): Would you send me -4e the Sellens A.C, short-wave adaptor eircuit. .. "A.: It doesn’t exist. An a.c. short-wave Adaptor, has been’ described in the 1930 ‘Guide. . 2. Would there be any hum when used on a seven-valve set? . A.: Very little. R M.D. (Helensville)-My A battery * charger from the 1929 "Guide" will not function. When I connect the "A" battery to the terminal, the rectifier flares brilliantly. Without a load everything seems correct. I have measured the voltage, which is right. : Are you connecting it round the right way, for it seems that when the load is applied there is no resistance be-

tween the terminals and a short circuit results, The positive of the charger, that is the lead ‘coming from the centre tap of the filament coil must be connected to the positive of the battery. If ‘you are doing this then try the effect of a series resistance in the positive lead. ° The, value of this should be about ten ohms, and it must be capable of carrying the current. E H.S. (Lower Hutt).-Is the rheostat * in the R. the W. circuit to control . the detector only ?-Yes. 2. How are fixed condensers connected in series to variable ones, and where do the wires connect. A.: You must connect a fixed condenser between either the moving or the fixed plates, and the external circuit. Say, in the R. the W. circuit you choose to connect it between the moving plates and the wire which connects to the low potential end of the aerial coil, You will lift this wire from the tuning condenser and attach one end of the fixed condenser to the now vacant terminal on the tuning condenser, and the connection removed to the free end of the fixed condenser. GPANKER (Waihi): I have a threevalve home-made set and wish to make an hf. adaptor using broadcast coils. Is the enclosed diagram suitable? A.: No. You must use a .5 mfd. bypass condenser between the plate of your valve and the aerial terminal of your set. A diagram shows the connection. To

‘stabilise this stage a grid resistance of 0 ohms must be used in series with the grid of the valve. 2. How many turns. would be required for the coils. AL: You do not state the type of wire you wish to use. For a .00035 condenser and 24 ds.c. wire on a 2tin. former without spacing you will require 68 urns, EN (Waverley).-I use four 201A’s and one C 509. . The tone is not good, nor can I hear distant stations. What would be the best arrangement of valves? A.: The arrangement and the bias (16 volts) is impossible. You need a power valve such as B605 in the last stage, with 135 volts "B." Lower than-this you will require 9 volts. If you are renewing, use the new UX221’s in all stages but the last. 2. I have three four-volt valves. Can these be used in my set with a four-volt accumulator? ; A.: Yes; but they would be no better than the present combination with a power valve. 3. The C terminals on my set are marked 43 and 9, but my OC battery has no nine volts tapping. Tf 164 volts too much? Iam using 135 volts B. A.: With C509, 164 volts is far too much. You could use a resistance in series with the battery lead or the cheaper way would be to buy a 9-volt O battery and use the big block for the B.

UNG (Waikato): Why cannot I get American stations with a powerful receiver and a good aérial? A.: You may not have listened when the American stations were! broadcasting, usually in the late afternoon or early evening, or you maybe in a bad locality. Watch the DX columns and see if anyone in your district is receiving them. If they are do some careful dialling during the times mentioned. . Would an aerial the sides of which are at right-angles be better than the L type for directional purposes, and what ‘length would be needed to make it: equal to a 90ft. L aerial? _A.: With an aerial of the usual dimensions direction has little effect. Your best plan if you wish to experiment would be to erect two aerials at rightangles, each 90 feet long, and use a switch so that either might be used. You could then see for yourself which was the better, You could try combining them. Experience has shown that there is little to better the 100. feet L-shaped aerial. 8. Is the lead-in included in the length of the aerial?-Yes, . 4. How should the lightning arrester be conected to the earth and the set? A.: It should be at a point where both aerial and earth contacts can be easily made. Neither aerial nor earth lead necessarily has to run from the arrester, but both can, if convenient. I M.L. (Timaru).-I have built a one- * valve amplifier: for my three-valve set, and enclose the eircuit. Can I use a switch to make the set work on three valves or four? A.: Your circuit diagram is correct, although there appears to be a great tangle of wires. You should: disconnect "speaker" and "B battery" terminals, applying a higher voltage to the one marked "speaker" than to "B battery." Put 60 on the latter, and the 120 on the former. The same applies to the "CO" battery. Only three volts will be required on the now first audio, and 9 on the pentode. 'The valve to use in the first audio should be a general purpose one such as 210 L. You could obtain an inter-stage jack and connect this in front of the audio transformer,’ but it would make your wiring more complicated. AvAXx (Waihi): I have an r.f. choke and am wondering if it is satisfactory. If not, could you give me details of construction of a better one? . A.: In our issue of March 30 "Cathode" went into the question of choke coils very

--i fully. Obtain a copy of this issue ang you will find all your difficulties clear up. 2, I find my set operates much clearer and louder with the © batteries cut out and the leads connected. Is this satisfac ory. A.: You are probably using too much © battery for the valve in question. It would .certainly be louder without a CG battery, but seeing you will ruin it. 3. hen I increase the "B" voltage on either detector or speaker there is a frightful howl: which I cannot eliminate, How can. I get rid of this? : ‘A.: Do not worry about the detector voltage as the coils are designed for low plate voltage. Try reversing the connections to the last audio transformer, and if this does not cure your trouble, embody an output filter. 4, I am using PM4 in the first audio stage. A.: This is incorrect. PM4 is a last stage valve. You should use PM3. QGUBSCRIBER (Timaru).-Who is the nearest dealer I can apply to for coils for my three-valve receiver? A.: L. B. Scott, Ltd., Christchurch State fully your requirements. . 2. Can an a.c. dynamic speaker be worked from a battery set and a B eliminator? A.: There are no a.c, dynamic speakers, Possibly you mean a high voltage d.e type, but you cannot work these from eliminators. 3. Are rotary converters silent and satisfactory ? A.: Yes; but write Moore’s, Ltd., Aucke land, for further particulars, W. (Masterton): What voltages * are delivered from each tapping of my charger? A.: When on load, the same as marked. , 2. Could the charger be used in cone junction with an electrolytic condenser and choke as.an A eliminator for three valves? A.: If you had a suitable choke with a very low resistance, yes, but the safer plan would be to use the six-volt tape ping with four-volt valves. . A: ©. (Christchurch).-I have a fours *valve set, and wish to make it alle electric. Will the tone be as good? A.: Yes, it should be better, with -the higher voltage -available. — . The s.g. valve will be heated, but I am undecided about the other three. Do indirectly-heated valves give any less volume than the others? -_ ---

-- k e . "7 . A.: The best combination may be selected from any makes, using the foljowing types: One 224, two 227’s, and one 171 or B605. ‘The indirectly-heated valves are much to be preferred. 8. Are the valves mentioned first-class? =Yes; don’t you read our lab. jottings? 4, When adding the fourth stage I had to reverse the leads to the primary of the transformer.. Is there a better way of overcoming the difficulty? A.: No; this is correct. 5. ‘Would there be any difficulty im adding a further push-pull stage of audio?-No. ‘A B.O. (Timaru): I enclose a sketch. * Which would be the better position for my aerial? » A.: The one marked 2. P, (Wellington): I am contemplate ing the construction of a small twovalve portable set. Can you recommend a good circuit? A.: Yes, the "Trampers Two," published in the "R.R." November 29 and December 26. 2. Will a coil assembly from an old two-valve set with condenser control regeneration be satisfactory? _A.: Yes, you must make provision for the regeneration condenser. 8. The set is to be used in Marlborough Sounds at Ohristmas time, with a makeshift aerial, What results should ge A.: The Marlborough Sounds sre notoriously bad for reception, but you ghould get phone strength with an aerial

D X. (Hawera): I am not getting suf- * ficient distance on my factory-made set. Is an aerial 110 feet long and 30 feet high a good one?-Yes. ; 2..I am using four 201A _ valves. Would a power valve make any difference é ; A.: A power valve suitably biased would greatly improve the tone, but not the signal strength. Such a power valve should be of the medium type. 4 8s 90 volts sufficient for the amplier?’ A.: 185 volts would be very much better. . 4, Do you a three-valve 8.g. set would be as efficient as the average four-valve set? . A.: The circuit is nothing extraordinary. It ‘would not be as good as the four-valve Browning Drake. 5. Where can I get the circuit diagram for my receiver? A.: Try the. National Dlectrie Ungineering Co., Featherston Street, Wellington. W, (Nelson): I-have a five-valve *factory-made set which frequently goes dead for some considerable time. If remove the © battery until the set howls, and then replace it, it goes satisfactory. A.: It sounds very much like a defective transformer. You can test the windings of these by the phones and cell, or phones and voltmeter test described in the 1929 and 1980 "Guide." Check for a loose connection. —

ANGATU. (Mangatu) : My four-valve Wi. set will suddenly stop, perhaps for a few minutes or a week or more, then it will suddenly come in at full strength again. I can always get a whistle when I tune in. . A.: This sounds very much trouble in the radio stage. During one of the silent periods bring the aerial to the fixed plates of the right-hand condenser and _ see if the set then goes weakly. If the fixed plates are connected to the ground then pring the aerial into the moving plates. Look in the radio stage for a defective connection. If the set has been built from a kit set with heavy busbar wire it is quite likely that there is a dry connection. Tug all the wires in this part of the set to see if any are loose. REFLEX (Dargaville): I am using a Daniells cell charger as an "A" battery and it is working satisfactorily. I formerly used it to keep a small acecumulator charged, but this has now failed to operate. Will the Daniells cell charger be satisfactory in conjunetion with an‘80-amp hour battery. A.: Yes, provided you kept it on continuously; but why go to the expense of an accumulator if the charger is functioning well as an "A" battery? FE (Wellington): Records come through well on my home-made receiver, but studio items very poorly. The upper notes of the cornet have often a very reedy sound, more like a clarinet, while certain speakers appear te have very seratchy voices. A.: It sounds as though the set is not properly tuned to 2YA, Reduce the volume until the signal can just be heard and move the dial until the exact point is found where the station comes in can be heard. Increase the volume, but do not use the dial as a volume cone trol. Put a variable resistance of 500,000 ohms across the aerial and earth if volume is excessive. Other suggestions are: Reverse the speaker leads and insert a 5000 ohms variable resistance in series with the B+ lead of the second audio transformer. SERVICEMAN (Hamilton): What do you consider to be the most useful set diagnoser for a serviceman. A.3 If you send us your name and address, as you should have done in the first place, we can put you in touch with one of New Zealand’s most prominent radio experts who ‘has one to dispose of. His yeason for selling is that he has now to use a bigger and more complicated piece of apparatus, The instrument in question is practically new. LAMBDA (Wellington): Would you give me the specifications for valve base coils for the Pilot A.C. Super Wasp? A.: Write Harrington’s Lid., Willis Street, Wellington, as they are the Wellington agents. 2. Would you give me the specifications for a wave-trap? A.: See the 1980 "Radio Guide." 8. What coils would be required for full scale coverage for each amateur band with the Super Wasp? A.: If the bands are being broken up with your present coils, place a midget

condenser ‘in parallel-.with the tuning condenser, and adjust this until.you get the bands to your liking.