Questions and answers

Radio Record, Volume IV, Issue 48, 12 June 1931, Page 42

Questions and answers

RYSTA (Nelson): What is the cor rect strength of caustie soda for an Bdison battery? A.: On these questions we advise you to write A, R. Harris and ©o., Chrisiehurch, who are: the agents. 2. Will strong solution damage the elements? A.: No, but it will not hold the charge. 3. What should it cost to charge a 6-volt 100-amp. battery through a Tunger charger, a unit of electricity costing A.: If the battery is well down avproximately 1/6 to 2/-. 5. There is an a.c. hum on my battery set on short-wave, and there is mo reaction however leads are changed and turns added. A.: It ig apparent that somewhere there is an open circuit. It will be a case of setting to and finding it. Try a 44 volts "CO" battery on the first audio valve and put $0 volts om the plate of that same valve. . TEKAWA (Te Awamutuj): What is the best type of valve to use in my set? , A.: Use the same as you have had in before with the exception of the last ews .

stage, in which we recommend 171. You could use Radiotron yalves throughout, QPSOx (Pico Pio): I have built the Sparrow Hawk One, but the set will a oscillate, but my "B" battery is old. A.:; It seems that herein is your trouble. Try reversing the turns to the tickler and increasing the "B" voltage, 2. Should I take down the tickler coil and wind it with finer wire to get on more turns?-VYes, 3. My aerial is 80ft. long and 30fr. high at one end and 20ft. high at the other and clear of all earthed object. Is it efficient? . A.: It is efficient, but would be more so if you could get it higher. HAND. (Wellington) : When will you publish the constructional details of the a.c. Outspan Five? A.: In the 1931 Guide, we published the constructional details of the Radiogram Hive, which. is really the a.¢, version of the Outspan, using a stage pushpul] amplification. ROMA (Wellington): Would the enclosed circuit be suitable for an auc. shortwave adapter?

4..% Yes; it will be as successful as any a.¢, shortwave adapter, though when #mateur constructed these are not always successful. It is safer ifeall hum is to be eliminated to make a battery adapter. . 2. What kind of a base is the Philips 035%-a.c. English. Ww H.T. (Christchurch): Your circuit ® is correct. Your style of neutralisation while not usual should be quite satisfactory. A tried circuit of the two valve B.D. was published in "All About the All Hlectrie." ’ (COASTER (Greymouth): My aerial poles are 30 feet high and lead-in 80 feet. If I made one pole say 55 feet high and lengthened my aerial to 100 feet would I get better reception? A.: Yes, you would get better reception but whether you would get the stations you desire cannot be said. 2. Does direction of an aerial affect the set A.: Not in the ordinary way. An aeriaj to be directional must have a very long horizontal portion in comparison with the lead-in. For this reason the Beverage aerial is highly directional. 3. My machine is a nine-valve commercial. Is it a good make for DX-ing?

A.: Xes, but good results in DX cuunot be relied upon unless one is in a fayourable locality. BEGINNER (Auckiand): I have an & valve 8.G. set. When I bought the; set 12 months ago each station was restricted to one number. Now they are spread over four or five. What is the trouble? A.: The lack of selectivity you are now being troubled with is due probably to the aging of the valves or your condensers being out of alignment, although any fault in the radio amplifier may contribute to decreased selectivity. U* (Te Kuiti): You are referred to Cathode’s article in the last two "R.R.’s" as you will find your queries are fully answered there. ON. (Auckland)-I have been troubled with oscillation in the »r.f. stages of my 5-valve set, although each stage is screened separately, I have tried all the usual cures. A.: Assuming that ¢vervthing ts O.R. aS you mention, and that all wiring has: been checked, it would appear that your / fault lies in a defective valve, an opeix secondary, or a failure to obtain a grouni

return, connections to a condenser re versed, and, failing all remedies place a 400-ohms choke or resistance in the grid leak of the first valve at the valve socket Why not use sg. amplification, and you.would probably get over this trouble? _ 2. What gauge of wire is best to use in a coil of this kind with a 3in. former? -24 d.s.e, ' 3. Is a chart like the one in the "Guide" procurable to give data for shortwave coils? A.: This chart ean be used, but a special one was prepared for "Q.8.T." about 12 months ago. 4, Can you give me the specifications for aerial and secondary and secondary and tickler coils for plug-in coils, not valve base? A.: See the last table of the list published in April 17 issue. Generally speaking, the aerial is about the same as the tickler. If anything, slightly less. BROWN (Auckland) : My B.D. after working for a while suddenly gives # plop and the volume diminishes, but can bé brought back to full volume by detuning the detector coil. i Hither the condenser is slipping or the grid leak has outserved its useful life. Maybe you have a defective grid condenser, K W.A. (Christchurch) : Is the Sparrow ¢ Hawk differential adapter as set forth in the "Guide" suitable for plugging into the detector socket of my 6-valye receiving set ?--Yes. 2. Would the super. het. adapter be better? .: No; you have not sufficient rf. amplification. UNCERTAIN (Christchurch) : Would you give me specifications for broadeast coils to tune from 200 to 550 m. to be wound on a 24in. former using 24 d.c.c. "wire for the secondary, 27 d.c.c. for the tickler and the primary to tune with "a .00085 condenser, and -will use a .00013 condenser for regeneration. A.: 70 turns on the secondary, 40 on the tickler and 30 on the primary. 2. The set will not bring in distant stations at sufficient loudspeaker strength. Aw I using the correct valves-they are two 609’s and one A609? A.: The more etnhcient broadcast coil that you evidently contemplate making will certainly improve matters.. You are using the best valves for the set_and you should get good results with New Zealand stations. How are your batteries? A M. (Canterbury).-Could you supply * details for constructing a resonator to tune my aerial?

A.: With your type of set it is not necessary unless you shunt a small yalue cona across the aerial coil and tune with is, ITHNSHUN (Carterton). — There seems to be a scarcity of old valves with 5 pin bases. Is there any alternaive A.: Yes, you can make them yourself by using cireles of three-ply and valve pins, However, the Kestrel Three, which is due out shortly, will not use five pin sockets. . 2. Is the "Eddystone" shortwave inductance unit obtained in New Zealand? A.: We do not know, and we have not heard of it being sold here. 8. I have a wet cell "B" battery which is charged with a ‘Tungar charger. When the current to the charger is switched off the resistance lamp and rectifying bulb light up. Am I doing any harm? A.: Only short circuiting your "B" battery. When you cut if off at the main switch break the connection between the charger and your battery. BROADOLA (Auckland).- Can you give me the coil specifications for .0001 variable condensers to tune coils on valve bases? A.> You have omitted to say what type of reaction you are using, and whit size of condenser. We presume it is a .00015. Furthermore, you have not stated whether it is secondary and tickler, or primary, secondary, tickler. As the former is the more usual, we advise you to try these specifications :- 85 to 60 metres-Secondary 14, tickler

35 to 80 metres-Secondary 14, tickler 20 to 85 metres-Secondary 5, tickler 5. 10 to 20 metres-Secondary 38, tickler 4, The secondary coil should be wound with 24 ds.c. wire or thereabouts, and the ticklers with 28 to 30-gauge d.s.c. wire. The windings should be separated by 1-8 in. T L.W. (Wellington): Why does my * set work better without a grid leak than with one? A.: Hither your grid leak or grid condenser is defective. Try another valve. 2. Where could I obtain instructions for converting the Sparrow Hawk one into a two-valve set? : A.: Build the Night Hawk Two, intructions for which were given in the "R.R." a few months back. 8. I cannot get reception without osciilation, and when I tune below the oscillating point I lose the station. A.: Try another grid leak as it seems that this is at fault. If you get to the bottom of the trouble previously referred to, you will no doubt get over this. Another valve may make a big difference. Ask a dealer to lend you one. IGHTNING (Auckland): 1 have two 30 amp hour accumulators and I run this in conjunction with a_ three-valye set and a cone speaker. I can only run the accumulator 380 hours without -recharging and I am told it is due to the amount of current taken by cone speakers. Is this so? A.: No, your speaker will not have any effect on the ‘‘A" battery current, or for that matter on the "B," as unless it is a dynamie cone type it draws power from the battery. Yours is not. Probably there is something wrong with your accumulator. Maybe there is an internal short circuit. It is possible that a sediment has collected at the bottom and the electrolyte wants drawing off and the battery washing out.

GHORTWAVE (Marton): I intend making a portable differential four. What is a good make of non-spillable accumulator and where could I obtain a miniature cone speaker for the above set? A.: Both these are questions you should refer to a dealer. If you cannot get satisfaction locally, write one. of the city dealers, who will no doubt be able to do something for you. 2. Must double spaced tuning condensers be used for the set if operated on shortwave? A.: No; while they would be an advantage they are certainly not necessary. They are undesirable if you wish to operate on broadcast. AUSSIB (Frankton): I have BD formers and condensers and a phasatrol. Can you give me a diagram of a circuit? + Yes, reproduced on this page is a circuit of a phasatrol showing how it is connected in a set. To operate, you

adjust to maximum resistance and then turn back so that the set will not oscillate when there is no reaction. 2. Can you give me the voltages on the fixed tappings on the Philips 3002 power unit? IL use two 201A’s one 200A and DH5. A.: Roughly you will have 160 volts on the last valve. We cannot tell you the amount you will have from the other tappings unless we know precisely the drain from each one. ‘The voltage is entirely dependent upon the drain. ECONOMY (Hakataramea): I have a four-valve battery set for long and shortwave. I am a shortwave enthusiast, but dislike hum of any description. How can I best use the electric mains for my A, B, and C supply and introduce a minimum of hum? A.: Employ a trickle charger for the "A" battery, use a good "B" eliminator, and if necessary employ a further choke and a 2 mfd. by-pass condenser in the

detector plate supply. This will eliminate all trace of hum. It is advisable to use by-pass condensers between all the "B--’s" and earth. These should be of as | high a capacity as possible, and should not be less than 1 mfd. 2. Some of the latest electric sets are humless. Is it all smoothed out? A.: The absence of hum is due mainly to high efficiency electrolytic condensers and chokes. However, much of it is got rid of by balancing. WW D.K. (Southland): My set is a * three-valver, and the "A" battery is composed of six cells in series parallel. It lasts about three months using the set about two hours a day. Would the Differential Three valve set be as economical as this? A.: Providing you use the same or equivalent valves, yes. It is the valves that take the current, not the set. 2. Would DEXL410 be suitable for the Sparrow Hawk differential adapter? A.: Yes, it will be quite satisfactory.

S HJ. (Waiuku) : What ratio of output * transformer is needed to match the Jensen 230 volt. a.c. speaker with two Osram 625A valves in push-pull? A.: We do not know the impedance of the Jensen, but it will probablv be that of the ordinary low impedance type, and will require a 25-1 transformer. If that is already provided use a 1-1 output transformer. . ; L J.T. (Auckland): Concerning the * L.W. with parallel output valves, why is the output transformer not placed in the main lead from the power pack? A.: Because it was found to go better where it is, However, you can try it in the main lead if you wish, providing your transformer will take 60 m. amps. of current, which is really quite usual. Actually you are employing a system of parallel feed to keep this heavy current out of the transformer. It may be necessary to use a radio-frequency choke of 1000 turns of 34 gauge wire between the 2 mfds. condenser and the power supply. 2. Are Cunningham valves suitable without any circuit alteration?-yYes. 3. Is an r.f. choke necessary with the 24.5's? A.: It will: probably help to keep hf. current out of the power supply, and should be placed where we indicated in answer No. 1. See the remarks published in last. week’s Questions and Arswers. Your circuit appears to be quite in order. . oj UMBO (Otago C.): What will be the inductance of a coil to tune to 600 metres’ using a .00015 condenser?-725 microhenries. B S.D. (Whanganui): In the layout ° diagram of the "Advance" a.e, shortwave receiver there are slight diserepancies in the accompanying diagrams. In the layout .01 condenser between the rathods and the screen of the r.f. stages connects to earth, whereas in the theoretical diagram it goes through the 500 ohms resistance to earth. The resister choke does not connect back to "B--" in the layout diagram and in the lead B-+- to screen detector stage a condenser connects to earth. In the layout diagram this js different. A.: Owing to the fact that diagrams had to be drawn before experimental trials were carried out, numerous minor alterations had to be made from tim? to time as found by experiment, and this has apparently led to one or two small

NORRESPONDENTS must attach this coupon to all queries sent to the Technical Bditor (Rox 103%. Wellington. Limit three questions, unless letter is accompanied by 1/ree. Name of set Number cf valves ..cccesecsccaceess Name tenes Stee ee mee eee Oe SEU eeBors Address POO CS HOHE EE HHH ESV ESE MeOEE® a i ee ee eed Tee HO Oe eH HEH EHESOHEOHSOBAIOOSOSOBASEE Nom de plume .lscevessesoeveeves To be kept in subsequent inquiries Date ....e.. eee eee eees Please Note:(1) Be specifie and briet, tabulating, if possible. (2) Write legibly, and on one side of the paper. (3) We do not design cireuils but aecept suggestions for feature articles, Solving trouble, as difterent from advice, is difficult by correspondence and while letters are given every consideration, answers are nol necessarily correct they are only our opinion based on the matter supplied which may be quite in adequate. Intricate and involver specifications cannot be supplier without a specialist’s fee. CRE OSE 0) RA) EE OE OD Ce OS Oe OR

n. the theoretical | dia-. the extra of 100,000-ohms | wot: shown in series with the -resistochoke. In practice the extra resistance may be reduced to ‘50,000, : Alteration: of: the of the 500 bias: resistor: in the vf. cathode has resulted ‘in’ this resistor being shown in two. places-@ fairly obvious error. "You say’ that: the Ol condenser is earthed through: the 500 ohm. resistor, but. examination: of the diagrams will show that it is earthed to the solder-tag bolted to the chassis. The 1 mfd. by-pass to’ ¥.f. gereen is. best earthed direct ax in the lay-out The: lay-outs

may be taken as correct, because -they have’. been. drawn from the laboratory. ‘New specifications ‘for. broadcast coil are given in the second edition of the: "Guide" ‘and will be reproduced next week. The r.f. coil:has now 166 turns of 28 enamelled, close wound, -topped from. the. bottom at. 23: and 78.turns, with three sockets in the ebonite top. A:thin flex with plug connecta to the F+. pin of hase. "The detector coilis 218. turns of 36 enamelied, tapped from the top at 8) and-145 turns, with three sockets: at top. The highest tapping on each btings. in. all. stations from 721 to .2BL: isielumve. -_-

QS. Using. 224 in the ri. stage ts not ‘the bias resistance 4000 ohms? : Yes, we take this opportunity to ‘out that in‘ the first edition of the "Quide" the. bias resister "for the 224 ‘was erroneously. stated: at 400 ohms instead .of 4000. . 8. Are ‘the. 100,000" ohms resistances for -the. screens of the r.f, Yee. detector valves of the 224 type?4. Does’ the 6 megs. d leak need for a 224 valve?-No. TD: (Kaitieke): I have built the Daniell Cell: arger, and it appears " ee electra mcrae)

be working. satisfactorily. How. often to should the sulphuric acid solution require ‘ renewing? ‘A.: Providing the cells operate satisfactorily it is only necessary to add a little sulphuric acid every month or so when the solution begins to look a little Epsom salts we have found to work quite satisfactorily. 2. Does the gediment on the zine affect the working? A.: Not to any extent, though it is well to keep the zines fairly clean. $..A coating of bluestone has crystallised on the inside of the porous pot above the sulphurie acid solution. If the zine touches it copper is formed. Should this be cleaned? A.t Yes, it would be as well to keep deposit of this nature cleaned off. Keep the copper as it is of marketable value. To prevent this forming above the solution cover the affected parts with wax. G B. BOY ( "4° stations be a straight line or a eurve? ' A.; Generally a curve, although if 8.U.F'. condensers are used and dial reading plotted against frequency, a straight line will result. 2. Is the Sparrow Hawk One an allwave set?-Yes, 3. Have particulars of the two-valve shortwave sets been published in the "R.R." or "Guide"? 4A.: Yes, the Night Hawk Two is an all-wave wet which can be used for shortwave only by the use of .0001 condensers for tuning and a. special shortwave choke. ‘ANCHOR (Matamata): It seems that you are paying quite a fair price for the receiver you mention. However, af it is in good order it should be a safe > Py) 2 (-7 }: Should a graph of © /

enough buy. Your set and speaker should be worth more than £20 to £25. 2. It is possible to add a pentode valve to the B.D., but it should be employed immediately following the detector valve without any further audio amplification. The B.D. usually employs at least two xtages of audio so that a pentode may not be advisable. . 8. What is a fair log for a seven-valve Radiola? A.: We cannot state, as ever so much depends upon your locality and your / aerial and earth equipment. TATIO (Invercargill).-Is it necessary to shield the. panel of the "Night Hawk Two" with aluminium? A.: It should not be necessary to do this though if you are troubled with hand capaeity it might be as well to do 50. 2. The transformer you mention is suitable for the set. BK. (Wellington).-Would you give * date for construction of a onehenry choke to pass a small current? A.: Tt should be built upon fin. core with the window of about an inch x 4. Wind on 2000 turns of 40 or similar finegauge wire, and take tappings out at eyery 250 turns, and try each one for best 2. I have tried several wavetrap cir- — euits in connection with my set, but cannot eliminate 2YA in favour of 4YA. Where could I get particulars of a filter for-my ? A.:-Our wavetrap has been used quite elose to 2YA, and has been effective in wsepayating it from 4YA, However, for

\ further particulars of your own set write i Technical Department of Philips amps. . . t ° ‘ ;

2. Is it possible to convert the radioplayer to shortwave by substituting the present coils. for smaller ones? A.: It is not practicable to do so. . Use shortwave adapter of approved ‘design. I find I can receive.a Japanese station best by disconnecting :the aerial from the set, and connecting the: earth wire to the terminal. Why? : The wires to the set from the are acting as an aerial, and ‘the natural wavelength. appears to be that of the particular station you: receive best. COL. (Waipukurau) -Is my set Pe: good. one?-Yes. 2. Is it possible to fix phones, to: this type of set? A,: Yet, but you could ‘not do"the job gO took if you do not knowexactly what for when you get: "beneath the 3. Can you suggest a suitable make of phones? , A.: Almost any make of first-grade phones w will do such as Brailes Siemens,