Questions and answers

Radio Record, Volume IV, Issue 6, 22 August 1930, Page 23

Questions and answers

B. (Dunedin) asks the following * questions relative to an h.r. receiver with five valves, two being r.f.:- _, _ 1. Will this set be all. right if it is full sSielded, and made (apart from this) ag’ described in, the "Radio Guide’? A.: Yes, it will be O.K., but you will need a balancing condenser across the detector main condenser, and will need to bring the return of the second r.f. valve to earth and A-. _ . 2. In aluminium lead what are :- ; {a} Working volts per cell-5O. . . 5) Voltage drop per cell..very small the electrodes' are kept small. (c) Size of plates per amp.-40 mas, per sq. in. (d) The best solution-Sodium-ammo-nium phosphate, and sodium potassium tartrate. . . (e) The approximate per amp, hour. A.: The question is not clear. The temperature should not exceed 100 to 110, deg. Fahr., and if this is observed the charger will continue. to operate until the energy is absorbed from the chemicals. Do not charge more than 22 cells in series, = C. B. (North Auckland) has been using ¢ anr.f, booster in front of a 4-valve set. He has now replaced the valves in the set with modern ones, and finds that it will work better without the booster. In fact, the booster is now not worth while. A.: Increase the filament voltage on the 222. Itis probably not enough. Decrease the screen voltage until the s.g. valve oscillates. af T. (Main Trunk) has a 4-valve screen * grid all-wave battery set, and finds that it will work with very little drop in volume, without an earth, A.: You have not stated whether or not you are using an eliminator. If this apparatus is used, and earth will be secured to the a.c, mains. Otherwise it would appear that the earth is being obtained through the capacity effect of your batteries and aerial, ; 2. When a grid-leak of a higher value than half a megohm is used I. can hear a squeal in the speaker, though ‘it is absent in the earphones. I have tried four different speakers, and they all equeal.\ A.: Rt appears that you are overloading the valve and causing audio- oscillation. 3. Is it possible to make this class of set more selective than with the use of a wave-trap? A.: Try a .00025 fixed condenser in series with the aerial, and a smaller value grid condenser. Why is it that some nights all stations can be heard when the second dial is turned from 0 to 100, providing the first dial is set to the station’s frequency? A.: It seems that the grid condenser is at fault, or that there is a broken connection in the detector grid circuit, or you are using a poor valve. ’ TZARNER ‘(Rotorua) has several burnt-out audio transformers, and Wishes to try rewinding them, He asks the following questions :-- 1. What does 2-1, and 3-1 mean? A.: This indicates the ratio. The higher the ratio the louder the signals, and the more the distortion. The converse is true for the lower ratios. It

theoretically means that ‘the ae, input will be magnified three times in the a.c. output measured in rms. volts (this is for a three to one transformer). i 2. How many turns and. what’ wire would I need to wind a two to one transformer? A.: This we cannot tell you, as transformers are designed to carry the current for particular classes of amplifiers, and you have not stated how much current you wish the transformer current to pass. If you intend to rewind several transformers, we should advise you to put a revolution counter on the spool as you undo the turns, and then wind back the same number of turns with the same gauge wire, If you wish to decrease the ratio and increase the current carrying capacity, increase the number of primary turns, bring the wire up another gauge, and decrease the num: ber of secondary turns. By comparing the numbers of turns on the

original transformer with those. you ‘intend to wind on you will get some idea of the ratio. 8. Is there any publication giving full particulars of transformers? A.: The manufacture of audio transformers is almost entirely restricted to large scale manufacturers, and. so there is little or no literature on the matter. With power transformers the case is different, and literature is readily available. However, try the Te Aro Book Depot, Wellington, who might be able to put you on to some publication. #{OPHFUL (Timaru) has a 4valve screen. grid receiver, but cannot get the first stage to work. The set bursts into oscillation very readily, and becomes unmanageable, ‘A.: coupling is taking place between the plate of the first valve and the grid of the last valve. Use -a larger R.F. choke in the plate lead to the screen-grid

valve, and increase the screen voltage. to 5 or more. Try a by-pass condenser hetween the rf.c. and the filament of the: valve, T F.C. (Christchurch) has a 4-valve * Browning-Drake, and although he has a good aerial:he does not get-the re sults he should. we A,: The question .is all too vague for us to give you any material assistance. Look through the trouble tracking section under the heading of "Weak Signals" in the 1930 "Radio Guide." There are really dozens of things that might be wrong. 2. When charging on a battery the hum wil Idie down and then Come up again, What is the cause: of this? , A.: It is probably due to ‘the resistance offered by the battery varying: as it is taking the charge. _ . When increasing the detector voltage from thme. B batteries a lond rattling and harsh whistle are heard. If I do not do this there is hardly any volume. A.: Your question is not quite clear. You would expect some noise when you are actually making the connections. Do you mean to say that when the connection is made to a high tapping that although the signals are improved there is a, noise? If this is the case it would seem that your batteries are too flat. Try a one mfd. condénser between B-+- detector . and A-. Look to your grid leak and grid condenser. 3. Why is a rheostat used on the 4 valve Browning-Drake? . A.: It is really a quite efficient means of controlling the volume and at the same time saving battery consumption. 4, I am within a mile of the local station, through which I cannot get any other station. What can I do? A.: It will be necessary to use a wave trap such as the one described in the "1930 Radio Guide." . R T.. (Hawke’s Bay) finds that if he * connects his gramophone pick-up to the grid of his detector valve all that he ean get is a loud hum, but when connected with the plate it works well. He is, however,. troubled with a. high level of scratch noise. He asks where he might obtain particulars of a scratch filter. A.: You have not stated your method of.connecting to the grid of ‘the detector valve. "We suspect that you. have been connecting one of the pick-up leads to the grid-leak instead of to the grid of the valve socket. This, of course, would cause a strong hum. If the connection was not properly made to the grid of the valve the hum would'‘still result. scratch filter is being described by "Mege ohm" this week, ' Co, oJ W.F'. (Dunedin) wants-a diagram of ° connections for adding another radio valve to a 5-valve commercial neue trodyne, His reception is weak. , A.: It would not be practicable for an amateur to add another stage. of radio frequency to a 5-valve set. It seems ag though the cause for weakness lies | élsee where. If you can get a copy : of the "1930 ;Guide," go through the _ points enumerated under "Weak Signals;" and you-might possibly locate the trouble: 2: Will a smaller grid condenser thay 0003 enable me to separate the stations below 3YA, as they are a: little crowded, A: Dry a .00025, .

tA C: (Nelson) asks if there are two Me types of 171A valves, as he has geen in the "Guide" where one uses 14 golts a.c. on the filament, and the other A: Volts in the text should of course gead watts. The table makes this clear. 2. What is the difference in construction of a power and a 201A type valve? A.: The main points of difference are the longer and thicker filament in power valves, the grids, which in general purpose valves are of thin wire and close together, and the distance of the grid from the filament, for the smaller this is the greater will be the amplification and the less the ability to handle strong sigmals. The size of the plate has a yery big effect on the valve for power valves usually have much larger than general purpose ones. A larger plate made ‘hotter by greater voltage draws more current. 8. How are the differences in impedf@ances arranged? A.: They are due to the spacing of the elements and the size of the grid and filament. 4, Is it on account of different valves being filled with different gases that the impedances vary? A.: Only in special valves is there any gs Almost invariably in general revalves there is a vacuum. [DTAMOND (Christchurch) asks which valves should be used in an a.c. reseiver. A.: We do not draw comparisons be‘itween commercial products. The three types of valves mentioned by you are quite good, but in the case of the nonAmerican valves see that you get the .exact American equivalent if you decide to use that make. ’ iD J.S. (Takaka) has a five-valve com- * mercially-built r.c.c. receiyer. There is no © battery and reception is weak. How could the signals be strengthened, and how can a C battery be added? » A.: It appears as though one of the grid leak resistances used in the 7.c, amplifier has broken down, and without a supply of these to test by trial and error, or an accurate instrument, it would not be easy for you to locate the trouble. If you wish to experiment buy a few grid-leaks of the following values: 100,000 ohms., 250,000 ohms., and 4-megohm. ‘Try these in place of

those already in the set. To insert a © battery find the grid return of the last valve, that is "FE" or "C-’ on the last audio transformer. It will be the only eonnection running from this piece of apparatus to A-. Break ¢he connection and attach enough leads to reach to the © battery. If you use a medium power valve in the last stage you will need about 9 volts bias, and with a suitable battery connect C-+- to A-, and C- to the grid return of the last valve. 2. My valves are about 12 months old. Would this cause the drop in volume? A.: No doubt it would have an effect. We think the real trouble lies in the resistances., ; 3. The makers stipulate’ 201a’s, Will 221’s do?-Yes. 4, Would an H.R. 4-valve receiver do better? A.: It should do. 5. What is the value of a condenser with six moving and seven stationary plates 3in| in diameter? A.: Probably .00025. MicRo-AMP (Gisborne) asks for data on resistances to convert a 0-25 volts a.c. meter (26 ohms per volt) to 250, 500, 750, and 1000 ranges. A.:- The following resistances are re quired : 6250 ohms, 12,500, 18,750, 25,000. ‘hese will be approximately correct to about 4 per cent. 2. Will the resistances require to be non-inductively wound ?-yYes. 3. What would be the resistances to use with a 0-250 volt 1000 ohms per volt

d.c. meter to increase the range to 500, 750 and 1000? A.: 250,000, 500,000, 750,000, 1,000,000 ohms. . Hach would be required to pass no more than one mil, How would a meter reading 0-10-100 mils. be increased to read 100, 200, and 500 mils.? ' A.: We could not tell you this without finding the resistance of the moving parts of your meter. This wouid be probably a few ohms or less. ‘The best method is to shunt a 0-10 rheostat across the terminals and adjust it until it reads eorrectly to your requirements, One method of doing this is to arrange the meter in circuit so that the fuil drain is passing through it, then connect the meter in parallel and adjust it until the reading ‘is some fraction of the whole. The range can then be recalibrated. Where can one procure accurate re sistances? A.: Of those you mention the Wlectrad ean be procured from at least Ballinger and Sons, Wellington, and Johns Ltd., Auckland, but they are probably procurable at most dealers. J H.C. (Sandringham) would like to * hear from any Auckland constructors who have made eliminators or similar apparatus described in the "Record." He would like to compare notes for mutual advantage. His address is "J.H., c/o Freslo Press, 25 Swanson Street, Auckland." Telephone 45-398.

(CURIOUS (Westland)-Is it. possible — and practicable to connect earphones © to an all-electric 8-valve receiver? | A.: It is quite possible, and can be done by first locating the voice coil of the dynamic speaker. Trace this back to the stepdown _transformer, and from the set side if this brings out two leads, These must be taken through the primary of a 1-1 transformer, and the secondary can be led off to the phones. The voice coil zoes to the cone of the speaker. 2. Can you tell me which two sets you would favour from the following (and here the correspondent enumerates several well-known receivers) ? A.: We cannot differentiate between factory-made machines. It is even difficult to tell you their characteristics unless we know the particular models to which you refer. We have tested and reported on B, but have no technical data on the others. L W.S. (Te Awamutu) asks how a cone9 speaker might be connected to an a.c. Console set. A.: See the reply to the above. correspondent. T H.O. (Runanga) asks concerning the % erystal and two-stage amplifier described in the 1929 "Guide," whether the erystal ig ~onnected into No. 3 tapping. A.: No, the erystal is connected to No. 2, and the speaker to Nos. 3 and 4, Disregard Nos. 1 and 5. By doing this your amplifier should work. BATTERY (Hokianga) asks if it would be possible to add an additional sereen-grid stage to a 4-valve Browning- . Drake. A.: Yes, the data in the 1929 "Listeners’.Guide" should be sufficient. It would be possible for you to find out the circuit constants from the 2 r.f. Browning-Drake and the adapted screen-grid BrowningDrake. 2. We are supplied with 230 v.d.c. mains. Would it be possible to convert this set to an all-electric, and what would roughly be the cost. A.: As we announced previously, we shall describe a d.c. eliminator for "A" "B," and "C" batteries. We publish with it directions for making a completely mains-operated d.c. set. This we will publish in a fortnight. Unfortunately we cannot tell you definitely the cost, but it should be about £3. You could use a rotary converter and an a.c. set, but the cost would be about £20.

M (Napier) enclosed two stalloid ¢ ‘stampings, and wants to know if these will do in the Lofting-White amplifier. A.: They can be used for the power transformer and the choke if they are regarded as 14in. stampings. The same number of turns will apply as have been given for this in the 1930 "Guide." 2. Could the transformer and a choke be made following the directions in the "Guide" without further directions for using this type of core stamping. A.: The stampings in the "Guide" are a different shape. You would need first to work out the amount of space your transformer will take, but it should go into the window provided quite easily. The core is assembled by pushing the centre leg of the larger stamping through the centre of the wire, and then from the other side pushing in the short one until they meet. ‘The spool of course will be 14 x 14 x the length of the window. The second layer of stampings will be arranged so that the short leg falls over the longer one. I/t is then an alteration of short and long on each side. Shellae the stampings well and the transformer should be quite a good one. Before putting the power on to the filaments of your a.c. valves, borrow an a.c. volt-meter or a moving iron d.c. meter, and test the low voltage delivered. Note-We are sorry we could not answer your question before, but there were about 50 in ahead of you, and each inquirer must take his turn,

PUZZLED (Auckland) wants to know, the current taken by his 5-valve set. A.: You could have looked this ;‘up from the "Radio Guide." We make it to-be about 14 mils if you have‘ the maximum voltage and the appropriate ias 2. I am using an electrolytic "B" power suit rated at 185 volts, 40m amps. Is this sufficient, at when I turn on the r.£. valves the loudspeaker makes 4 throaty noise. A.: It should be quite satisfactory providing the solution is kept up to the right strength. For further information on electrolytic elimination see 2 dealer who handles them, W F.H. (Westport) wishes to know * the voltage delivered from 3002 eliminator. A.: This- depends upon the drain. It will deliver 150 volts at 30 mils, maximum tapping, We cannot tell you what each tapping will give unless the drain is known, For a pamphlet on this eliminator write Philips Lamps, Hope Gibbons Buildings, Wellington. Can I charge an "A" battery by adding a Bell stepdown transformer to the high voltage tapping of the above eliminator. A.: No. You would require a separate transformer and a rectifier. The current delivered by the tappings on your eliminator is d.c. and you could not step it down with a transformer. It could be. broken down with a resistance, but it would not supply nearly current enough to charge your "A" battery. A "B" eliminator and "A" battery charger combined can be obtained. The New Zealand agents are J. A. Smyth and Co., Victoria Wellington. 3. Where might I obtain test tubes for making the wet "B" batteries? .

ISTENERS must attach this coupon to all queries sent to the Technical Editor (Box 1082, Wellington). Questions arriving ' without it are likely to go astray or be delayed. Name of set ceocscoccveccccessesvece Number of Valves cocesscecccescoce Name PeaF OSS SOS EOS HOOELOZELES BODO Address eee ee oe oe ee ooeovoosoessarD Poe e OPO Oe eeoecssoreceneoe gecocsoesoraees Nom de plume ..ccescsescscecscccece To be kept in subsequent inquiries. Date cccccccvcccsscccsesscesscosess Please Note:(1) Be specific and brief, tabulating, if possible. (2) Write legibly, and on one side of the paper. (3) We ado not design circuits, but accept suggestions for 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. Se QP re

A.: G. Wilton .nd Son, Willis Street, . Wellington. 4, Could you set aside a page for amateur transmitting and give a circuit for the working man’s pocket? , ~A.: Amateur transmitters are well catered for by their own magazines. If you want help in this respect communi» cate with Mr. §. Perkins, Puru Crescent, Lyall Bay, Wellington, who is the Dominion secretary for the N.Z.A.R.T.A. G R. (Eltham) is getting fair results ™* with "Round the World Two." He would like to correspond with a constructor who has built his set.. His address is "81 Conway Road, Eltham." SUBSCRIBER (Oamaru) asks what is the best height and length for an aerial, His present one is 30ft. high and 80ft. long. Would be get better results with higher poles and a shorter’ aerial? A.: Generally speaking a high short aerial.is better than a lower and longer one, although the latter is usually better when there is a great deal of static about. 2. Would a higher aerial lessen: the amount of noise? : No, it would increase it if anything. 3. Does direction have any effect. _ A.: It does under certain conditions. See the "R.R." March 21 and FAIRFAX (Otane): What would be the best combination of valves for my. 3-valve set? A.: Detector, Radiotron 112, Philips A415, Mullard 4DX, Osram L410. First audio the same except A409 and PM8. Last stage B406,.PM4, P410. . 2. Could a pentode valve be used in the last stage successfully? A.: It would probably be satisfactory. 8. Will a joined lead-in affect signal strength? a Not unless the joins are unsoldered. "VY S. (Auckland): I cannot get the s.g. * receiver described in the "Guide" to oscillate below 38 metres. A.: Deerease the screen voltage and increase the detector voltage. If neeessary wind more turns on the tickler. 2. For the audios I use two 605’s. Is this rieht?

A.: No, a 409 should be used in the second last socket as 405 takes a very heavy current and is designed for last stage operation only. 8. Will the set work with "B" power pack? A.: Yes, quite well. 4, Is last year’s "Guide" procurable, and what is the subscription rate to the "RR"? A.: A few copies of the 1929 "Guide" are still obtainable for-2/9 posted, while the subscription to the "Record" is 12/6 posted in advance or 15/- booked. W D.W. (Dunsandel): I cannot get * any foreign stations with.my 9valve receiver. . A.: You should do. From the sketch of your aerial it appears that it is altogether inadequate. You will need another Wole, the height of the pine at the house-dnd. You will further’ need more insulators on the tree-side of the aerial. See our article on aerials published in the "R.R."’ March 21 and 28. PETONE (Petone): In the DX and Shortwave Notes the prefix "R" and "QS" are given to denote signal strength. What are the values of these figures? A.: They will be published in this week’s ‘Shortwave Notes. 2. How can I compare different standard times with our clock? A.: ‘The time officially adopted for a eountry or a portion of a country is usually based on one of the 24 standard meridians which start with the meridian 6f Greenwich and extend 15 deg. apart around the globe. The local time on each of these meridians differs from Greenwich time by a whole number of hours, thus American Pastern time taken from the 75th meridian is 5 hours behind Greenwich or 16% hours behind

ours. The Central time is taken from > the 90th meridian and is 174 hours behind ours, while the Pacific time is 194 hours behind. This could be ascertained from our DX clock considering San Francisco as Pacific time, and New Orleans as Central time, and New York as Bastern time. 3. I am having oscillation troubles on the broadeast band of my s.c, a.c. allwave set. . ; . A.: You will need to see the Weliington agents for that particular receiver and ‘put your case to them, Usually all-wave sets compromise on either of the bands, but it appears in your case that there is something wrong, and it is most unlikely that we can advise’ you satisfactorily without having seen the receiver. . M H.M. (Christchurch): I enclose a * circuit of a 2 rf. a.c, BrowningDrake. I would: appreciate criticism. A.: Your circuit appears quite good and you appear to have the number of turns on your coils correct. 2. Will I lose any efficiency by ganging all tuning condensers? A.: You will lose a little, but they are well worth ganging. 8. I understand that Philips a.e. valves, American series, are directly heated. If this is so, why cannot I use ordinary d.c. valves? , A.: Philips have the equivalents to the American indirectly-heated valves. You could not use- d.c. valves in the

radio audio stages. An a.c. directly-. heated valve has a very much heavier filament than its d.c. prototype. If you wish to use 4-volt valves use the H409’s with ©415 detector and B406 as output. [GNORANT (Waipori Falls) : I cannot get good results from distant stations. Reception is fuzzy and distorted. My aerial is about 47ft. high and, including the lead-in, 80ft. _ A.: The distortion is due probably to a defect in your set. Communicate with your dealer. Your aerial is quite good. X-er (Waihopo).-Could I expect good results from a 2 r.f£H.R? I submit a sketch for your consideration. A.: The two should be almost . equal in sensitivity, while the H.R. would be easier to handle. Your sketch is quite good. . 2. Will an extra stage of rf. in the form of a separate unit be sufficient? A.: It would be worth trying, but you would probably have to build a set like the two r.f. Browning-Drake, that is, with each unit completely shielded. R J.G. (Auckland) : How can a crystal * set eliminate an amateur transmitter 200 yards away? A.: Probably by changing the direction of the aerial, which should be at right angles to the line of direction of the transmitter. Another coil and condenser would. probably be effective. Can a i-valve short-wave receiver be built? If so, where can I get the particulars? ; A.: Build "Round the World Two," using only the detector stage. Use telephones in the place of the audio transformer. Note: We have referred your other query to the DX Hditox.

G C. (Dunedin): Will you give me * the number of primary turns for: certain valves (here the correspondent enumerates a list’ of receiving valves)? .: You can work them out for yourself from the following formula :-- Se P= 200,000 v= Ri. Where P — number of primary turns. T — number of secondary turns. Ri — the impedance of the valve. 2. Will it be satisfactory to eonnect the two r.f. condensers on the same spindle with a trimmer across the’ first r.f. condenser and another: trimmer across the detector? A.: Unless you are seeking maximum efficiency with almost as many controls as a three-dial receive+, it would be better to put the trimmer across the detector only and connect all three on the one spindle. 8. Is it necessary to put an amperite across the valves, and a 500.00 ohm rheostat between aerial and earth? A.: You need put a rheostat in the valve circuit only. when the valve is of less voltage than your accumulator. It would not be across the filament circuit, but, in series with it. The resistance across the ‘aerial and earth would be a good volume control. AIKO (Turua).-TI cannot get the re~ action to work properly with my 2 r.f. Browning-Drake. It gives me splendid results otherwise? A.: Try the swinging coil method of applying reaction. 2. I do not understand clearly where the 200,000 ohms resistance to control the r.f. late current should be placed. A.: They are placed in series with the B plus rf. tappings. The by-pass condenser is shunted across the resistance; rf, and’a.f. current should not be drawn from the same tapping unless an r.f. choke js in series with the r.f. leads, and the set side of the choke brought to B minus.

‘H.M. (Kingsland)-My commercial. ly-made receiver is selective on the shorter wavelengths, but the stations spread out a good deal on the longer waves , A.: Try a .00025 fixed condenser im . series with the aerial. 2. Could I add a stage of push-pull amplification? « My last valve is a 171, but there is an output filter. . ' Av: If you use first-grade transformers it should be all right. , . 3. What is the maximum undistorted output of two 245’s in push-pull-4.8 watts? \ 4, Would Pilot giant transformers be satisfactory ?-Yes. 5. Could I use a-volume control across the primary of the in-put transformer as well as the original volume control on the set?-Yes. . A2RIALS (Napier).-Which is the bet ter aerial, an "L"’ aerial 40ft. long and 80ft. high, or a "T" 100ft. long and ~40ft. high. . A.: The effective length of the ‘I aerial is almost the same as the "L" aerjal so that there is really noo difference between them. BATIERY (R.D., Balelutha). — A crackle has developed in, my 5 valve receiver. I cannot locate it. A.: It seems to be a broken-down condenser, but possibly it is your speaker. 2. Gould I expect better results were I to change to a 5-valve BrowningDrake? A.: Results would be better, but you would have more trouble. 8, Results. would be better, but you would have more trouble.. 3. If I made the Browning-Drake could I use the parts? A.: Yes, but you would need fresh coils, of preferably 2in. or 24in. formers. . What valves- do you recommend in the radio stages? Mullards or the new Radiotrons? A.: There is really little difference between them.

_ How many turns would be required lor the coils for the Browning-Drake? A.: They are given in the "1930 Radio Listeners’ Guide." , APRIL (Greymouth).-The signals come through my set irregularly. Sometimes they are loud, other times ine audible, A.: A fault such as this is difficult to locate when the set is not to hand. Your only method is by searching, preferably with a continuity tester, It may be a broken-down condenser. 2. I intend building a short-wave reeeiver which would give loudspeaker reception from all parts of the world. Where could I obtain a circuit, how many yalves, what would it cost to onerate, and what would be the approximate cost to build? ‘ A,: We can recommend no better than the 4-valve screen grid receiver described in the "1930 Listeners’ Guide." It would: cost from £10 to £12 to build, and operation costs would include say, two- sets of B batteries a year and the constant charging of your A battery. ; C W. (Christchurch) : Should I be able * to get American stations with a commercial receiver. with a gobd aerial. _A.: If you looked for them at the Fight time and your set was sufficiently tuned up you probably would get them. BE: (Oamaru): Would you send ® me a. diagram for a one-valve shoriwave adaptor to plug in ‘a six-valve set? A.: An adaptor was described in the #4929 Guide," but -omit the ‘by-pass condenser between: the -plate and A-+- shown in the ones ‘diagram, ‘The. theoretical is eorrec . YALE (Wairoa): I like to. listen. to 2BL on Saturdays, but am interfered with by 1YA. Can this be remedied? A.: Only: by the usé of a‘ wave-trap. 2. Is there any way of eliminating or modifying blasting noises? A. A properly biased set should not blast. Check up and see if it is not the ptation. SUBSCRIBER (Christchurch) : Where could I obtain information as re gards electric clocks? A.: The Te Aro Book Shop, Wellington, has a volume priced less than 2/6 which would suit your requirements.