Questions and answers

Radio Record, Volume IV, Issue 18, 14 November 1930, Page 14

Questions and answers

B S.D. (Wanganui): If glue is acci- ¢ dentally put on the enamelled or s.¢c.c. wire when making a transformer will any damage result ?-No, 2. Can a winding be placed on the Loftin White transformer to supply 6% volts, 4 amp. to a speaker through a dry rectifier ?-Yes. 3. What are the specifications? A.: 82 turns 20 gauge wire.. You will need a rheostat to exactly obtain the voltage. 4, Will the L.W. and tuner give distance and volume equal to a 5-valve neutrodyne? . A.: The three-valve Loftin is about equal to a five-valve ordinary neutroyne, R R. (Akaroa): Can a five-valve set be * made from a three-yalve? Where might the parts be obtained? A.: A five-valve set can be made, utilising the parts in your three-valves. The balance might easily be obtained from any dealer. If you want a straight five try the shielded five neutrodyne described some time back. Better still, try the B.D. or Hammarlund Roberts, from the 1980 "Tisteners’ Guide." WAaxBAck (Bay View): How is the | salamoniac solution referred to in "Hard-up’s" article of June 6 made? Av: The tablets are bought and dis- solved in rain water.

2. Is a malathoid compound essential? . A.: No, but it prevents the acids eatire away at the joints. GNEDDO (Whangarei) : Using 84 turns of 24 s.w.g. wire on a 2in. former tuned with .00085 condenser, at what turn does the neutralising tap come?About the twenty-third. 2. Using two stages of r.f. shielded in the above secondarv coil what is the corxect number of primary turns for 201A and 630 valves? A.: 201A, 15/16; 680, 25/380. 3. Why does the insertion of .0001 series condenser disturb the stability of a four-valve B.D.? A.: This is not unusual. It alters the grid to earth capacity and introduces damping. T[WO-STROKE (Gisborne): Can you suggest a remedy for motor-boating in my seven-valve R.C.C. set? I am using as second audio Philips 630, as first audio 615, and as detector 609. A.: You have far too much amplification; 615 should be in the detector socket, 609 first and second audio. You. may have trouble in the resistance units. You would have to test for this by taking voltage readings at various points, TPERMINAL (Dunedin): I can bring in morse stations on my _ short-

wave adapter, but nothing elsé. The set will not oscillate on some of the coils. A.: Increase the number of turns on the reaction coil, 2. When the end of the grid-leak is touechcd there is a terrific hum. A.: This is quite a normal state of affairs and shows that- the audio end is in order, 8. In a theoretical diagram the secondary condenser goes to the secondary coil end of the grid condenser, but on the wiring plan it connects to the other end. A.: The theoretical’ diagram is quite correct and is always published as a check on the lay-out diagram, in which there is always a possibility of a mistake. 4, Would a turn more or less than 150 on the radio-frequency choke affect its efficiency ?-No. 5. The valve of the adapter is slow to light up compared with those in the receiver. A.: If it is the same make, look to your filament extension lead. If they: are of ordinary flex and are connected properly everything is in order, but if there is any material resistance in the connection it is going to have a hig effect upon the voltage and consequent'y will impair the working of your receiver, Are you quite certain you have the filaments connecting into the right pins? If you had them going to filament and cathode you would get just half the voltage. This would cause the symptoms you speak of, I B. (Christchurch): How many car 4° batteries would a 8 to 6-amp. charger described in the "Record" charge at one time? A.: If you used the 6-amp. rate with 14 gauge secondaries you could charze two batteries in parallel. If you increase the secondary voltage to 12 you could then charge two in series, 2. How many 6-volt batteries each 39amp. hours would it charge at one tima? A.: It all depends upon the winding. You can wire the secondary to take any number of batteries. . P K.D. (Oamaru): Would a double * aerial 100 feet long and 40 feet high be superior to a -single-wire aerial of the same dimensions?-No. | 2, Are two ground wires an impreye ment? A.: Yes, but they should be as short as possible. 5. Does a small dynamic speaker require as much power as a good cone speaker? A.: A cone "speaker dors not require any field current to energise it, whereas the dynamic speaker does. As far ag sensitivity is concerned.there should be little difference, V A.T. (Kaponga): I am not clear * about the use of a super heterodyne from an outside aerial, I recently purchased a loop, and it was not nearly as sensitive as the aerial. A.: There is no question that an outside aerial is more sensitive than a loop, but the fact of the matter igs that the regulations forbid the use of certain suner heterodyne receivers with anything but a loop. The model to which you refer, we are informed, has been passed by the P. and 'T. as suitable for use with an aerial. For best results this should be 50 or 60 feet.

8.L. (Taumarunui): I wish to re- * new my valves and would like to know if I can improve upon the combination already in the set. A.: You cannot; use the same make _ the same type of valves. ae 2. Can a screen grid valve be introduce ~ A.: No, it would not be worth the ex- : pense of redesigning your set. 4 R. B.T. (Whangarei) : Does the enamel on aerial wire affect the pick-up of signals? It occurred to me that it was an insulator, A.: It is not an insulator against high frecuency current, and by preventing corrosion is definitely superior to the ordinary type of wire, We will have an article on this subject in a fortnight’s time.

2: My set works better with the aerial and earth wires reversed. Am I doing any harm? A.: No. Yours is not an isolated case. YBoNS (Waikato): Can the a.f. amplifier be equipped with jacks so: that the detector one or two stages of amplification could be used as well? A.: Yes, but you might produce audio oscillation through complicating the wiring. 2. Would the amplifier be suitable for a 5-valve set?-Yes. : 8. What ratio of audio transforme would you recommend? 4. Would it operate with any type of detector or tuning circuit? A.: It will operate with any desired amount of radio frequency amplification with either leak or power detection. 5. What type of rf. amplification would you recommend for three-valve sets? .: A three-valve set -would be one -r& detector and one audio. Note: Your amplifier is not biassed and this is a bad mistake. Break the connection between the grid return and A- and insert a "QO". battery, with the negative toward the transformer. F,LECTRON (Oamaru): Would ‘you give me the data for coils for .00025 variable condenser to cover the 10 to 15 metre band? A.: A special article appeared on this subject a little while back. You will need 2 smaller capacity than .00025 to operate successfully on that band. 2. Has Mack’s Addaphone been tested? A.: Yes, about 12 months ago we had a laboratory account of it. 8. Is an adapter worth the outlay from the point of view of entertainment? A.: Yes, a. considerable amount ‘of amusement can be had from listening on short wave, and an increasing large amount of important broadeasts are taking place on low-wave lengths. -4, Are there are stations other than Morse between 10 and 15 metres?-No. 5. Will the enclosed diagram if made up give good results? A.: Yes, it is an ordinary Reinartz circuit. 6. Is a log of 58 broadcast stations poor? A.: It depends on what strength they have been logged. If it is in the centre of the town then it is quite good. P R.S.. (Auckland) asks several quese tions concerning our articles on d.c. mains eliminators, but a few of the points were explained in the last instalment which he had not seen at the time of writing. Regarding the series-paralleling of valves; this is quite in order, and the choke to suit these could be made with

34-gauge wire, with a lin. core, or the choke can be purchased ready made. Regarding the grid bias system, these have been fully dealt with, and of the two systems, that marked (a) is probably the better. The resistance can be varied as suggested. Screen grid valves introduce limitations, but these may be overcome with proper planning on the lines indicated. If experimenters get two or three straight r.f, stages going well, they can then experiment with the s.g. valve. The series parallel arrangement should not introduce hum. F S.J. (Tinwald).-During a recent hail- ¢ storm a clicking noise developed in my set. On touching the lead-in wire I received a violent shock. When I dis-

connected a séries of sparks jumped from the wires to the pliers about an inch away. What is the cause and remedy? A.: It appears that your aerial was highly charged by atmospheric electricity during the storm. You should have had a lightning arrester in the circuit, as you are running a grave danger of not only ruining your set, but incurring bodily harm. At the same time, examine the aerial, and see that it cannot establish contact with the electric light mains of any power wires. . . 2. Is mine a good set? © A.: Yes, it is first grade. A laboratory report appeared a short time back. an I make my set suitable for receiving short as. well as long-wave? A.: Yes, you can either purchase vr make a short-wave adapter, One was described in the 19380 "Guide." Boe (Wellington): At times 2YA breaks through in various places on my 7-valve set. Is this a peculiarity of the station? It does not continue for long and there are no symptoms. Two of the screen grid valves do not light as brightly as the others. A.: It is certainly not a peculiarity of the set and it may be due to a defect in the particular set you have. Have the voltages of your screen grid valves tested. Again, it may be due to waves reflected from nearby objects, but this is a rather fantastic explanation. VALVES (Christchurch) : Can my set using two 245 valves be altered to take two 250? A.: Yes, a set-builder could do the job for you, but it would be fairly costly. F R. (Petone): What station should I ’ be able to receive on my 4-valve set A.: You should get good reception from Australian stations. 2FC and 2BL should be particularly good ana there should be a reserve of power after about 10 o’clock at night. Would an aerial . long and 30ft. high running over an iron roof accouut for poor reception? A.: Yes, your aerial is not a good one. ‘The height is only the difference between your roof and the aerial wire. 8. The earth disconnected from the rth makes very little difference to recepion. A.: This is not unusual in a.c. sets. F N.K. (Dunedin): I have two aeriai * masts, one 43 feet and the. other 40 feet high. ‘I am using 60 feet of aerial wire and 40 feet of insulated leadin. Would it be advisable to lower one mast to 30 feet? A.: We can see no point in your low-

ering the mast. It would not improve matters. oe 2: What is the correct length of aerial to use, single wire for best results? : A total length of 70 or 80 feet is ample. . 8. Can phones ‘be connected’to my set and what would be the advantage of using them? A.: The advantage of phones is convenience only. On modern sets they are of little use to listen to weak stations for the noise is usually in an overwhelming proportion to the signal strength. They could be added to your set by taking a lead from the voice coil of your moving coil speaker, 4, When will the 19381 "Guide" be available, and what will be the price? A.: We are hoping to have the "Guide" available-in the beginning of April. Price 2/9

The Great Yacht Race ----

WING to the resourcefulness of the National Broadcasting Company and the Columbia System, American audiences (writes the Washington correspondent of London "World-Radio" ) received a remarkably fine account, episode by episode, of the America Cup races. Never before was such interest taken in an international sporting event as in Sir Thomas Lipton’s gallant attempt to lift "the old mug." The major broadcasting companies used every mechanical and ingenious device possible to bring a vivid running description of the races to every American home possessing 4 wireless set, and with complete success. "8 Ten-minute descriptions of the races at twenty-minute intervals were. given every day that Shamrock V and BEnterprise sailed the course. What was virtually a floating broadcasting studio was set up aboard the U.S. eruiser Kane. Microphones were placed at points of vantage on the deck, and the eruiser steamed with the racers on the starboard side. The U.S. coastguard cutter Champlain, similarly equipped for wireless, covered the port side, while overhead radio announcers gave panoramic broadcasts of the races from the dirigible Defender as they surveyed the thirty-mile triangular course. A fifty-watt short-wave transmitter on the Kane relayed the description of the races to a land receiving station, which, in turn, transmitted the account to the major networks. Announcers in the airship used a transmitter on the Kane relayed which had a range of twenty-eight miles. A total weight of 600 pounds was allowed for announcer, engineer, and equipment,

I HAVE just received a letter from Mr. M. Nakamura, Japan, and he gives some interesting sidelights on DX in Japan. I sent him a copy of the "Radio Record," and he was very interested in the way broadcasting was controlled here in New Zealand, and he also was very interested the way the "Radio Record" controlled the DX Club with the necessary information DX enthusiasts required. He states there are two types of radio broadcasting in China-the Government and privately-owned ones. He states the Government stations are regularly on the air, and the private ones come on at any old time. The: Chinese stations that are regularly on the air are COMK (410 metres), COHB (445 meters) COTN (480: metres), COPK (320° metres). The following Chinese stations have gone off the air:-KRS, SSC, GOW, NKS, ORO,

CBOS

S.

Ellis

(Okato).

Pott $ C a ee i i id PDP PDPPDDP DDO PPdndab ddd "+ PELL LS SI SILI AN increasingly large number of correspondents are sending envelopes and requesting that we forward them _ information through the post. Except under exceptional circumstances, we will not do this. Our service is maintained through the paper. We would, too, remind inquirers that a coupon taken from the "R.R." must accompany every question or series of questions. POCO PAPDPPPPPPDAPPPPPA

ISTENDRS must attach this coupon to all queries sent to the Technical Hditor (Box 1032, ° Wellington). Questions arriving without it are likely to go astray or be delayed. Name of Set .-.csercesaceooesesvace Number of Valves ..sssesrovcscecce Name dese ec eae stare pes osereone AGGreSS se vavccecrccecvocestoresoe OOo OOH HO HEHE OHS HEASF OAH TOSHOMHH OH OS SIONS ECO OSE RAHEMOSHAEHAMHS ESSE HTHOERHETSOHNEO Nom de plume . sieceusesesssunsenss To be kept in subsequent inquiries. Date cercccccsesccacters eeasccee eee a Please Note:(1) Be specific and brief, tabulating, if possible. (2) Write legibly, and on one side of the paper. (3) We do 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.