QUESTIONS AND ANSWERS

Radio Record, Volume VII, Issue 10, 15 September 1933, Page 27

QUESTIONS AND ANSWERS

ADIO BUG" (Rotherham): What is an omni-directional aerial? A.: One which radiates power equally in all directions. A mono-directional or beam aerial system radiates in one direction only. 2. I have a four-valve all-wave set,.and the dial is graduated from 0 to 100, Can you tell me how to pick up GSF? A.: We could not give you even an approximate idea, because we do not know the wave-bands covered by your set. For the same reason we cannot identify the station about which you inquire, Your best plan would be to get in touch with your dealer, and ask him to show you where the principal short-wave stations come in. M. K. (Wellington): My aerial runs in a -north-westerly direction. Wouid another aerial pointing north-east improve American reception? A.: It is very doubtful if it would, The average type of "L" aerial has negligible directional effect as signals are picked up chiefly on the vertical] lead-in portion. CHO" (jdawke’s Bay): I have two aerials which are taken to lightning arrestors, and then on to the set. Should I earth the aerial not in use during a thunderstorm ? A.: Not if it is properly connected up to the lightning arrestor. Note: An article on Beverage aerials appears elsewhere. ASH" (Christchurch): Two-volt valves will be quite suitable for your portable. The circuit of your onevalye set is correct. "NOt SURE" (Taihape): What would be the approximate cost of a filter to eliminate local power disturbance? A.: It depends upon the design of the filter, The cost would probably be somewhere around £1-or 25/-. 2. Would an X-ray apparatus in the locality cause a loud crackle during the day?

A.: Quite probably, though it could easily be proved whether it does or not by taking a note of the times when. the crackling occurs, and then inquiring from the owner of the apparatus whether these times were coincident or not with those when the machine was in use. 3. When my set receives a slight knock, a rattle is heard in the speaker. A.: There is a loose connection somewhere, "A RIEL" (Wellington): In a recent "Radio Record," the erection of a shielded aerial of 10 feet long is deseribed. Do you mean the horizontal length is only 10 feet or that the aerial! and lead-in are together 10 feet long? A.: Neither. he vertical aerial attached to the pole is 10 feet long. The down-lead from this aerial, shown by 28 heavy black line, is the special shielded lead-in. 2. Would a 10 foot aerial be sufficiently long to bring in the main Australian stations and KFI? A.: Yes. With your set you should have no difficulty in doing this. A E.B. (Hitham): I have a five-valve * commercial a.c. set. Broadcast reception is excellent, but on short-wave I have heard only four stations very faintly. Based on the formula given to "Maths" recently, the short-wave band covered by the set is from 107 to 214 metres (2800 to 1400 k.c,?) A.: You have heard probably all you will hear, as there are very few stations operating on this band in this part of the world. Your set is apparently an American receiver designed for reception of police stations, which employ wavelengths between 100 and 200 metres. "(XNURIOUS" (Pareora): I have constructed the A.V.C, Super, described in the December "Radio Times," but have not included the A.V.C, The set has been operating well, but recently developed a crackling just like static. A.: Hyvidently a broken-down or partly broken-down fixed condenser or resistor. 2. I substituted a 57 in the mixer oscillator stage. 4YA is much stronger. KFI comes in louder than 8YA, but 38ZC and stations at that end of the dial are much weaker, . A.: Your set should have been realigned after the substitution of the 57. "Yo" (Seddon): How could I fit headphones to my set? A.: Take a lead from the plate of the output valve to one side of a high test 3 mid. fixed condenser. Connect one tag of a pair of headphones to the remaining terminal of the condenser, and the other tag to one side of another 1 mfd. condenser. The other side of this goes to earth, 2. My present "L" type aerial points due west. Would a similar aerial pointing north-east improve reception from American stations? A.: See reply to M.K., given above. Note: An article on Beverage aerials appears in this week’s issue. G 8S. (Auckland): I have a four-valve * a.c. commercial set which employs a reflex circuit. Selectivity is poor, I intend remodelling this set and adding an-

other stage of x.f. Could you recommend me a circuit, which would use. most of the parts (list enclosed) ? Cn a A.: If you wish to build a set with two stages of r.f., such as the "Sky Line Five" (described in the June "Radio Times"), you will need a three-ganged condenser. You would be able to use most of your parts to build the "Midget Four," deseribed in the September ‘Radio Times." "TN DOUBT" (Masterton): Substitute the 227’s. with 56’s, 224’s with 224A’s, and replace the 171A’s and S80. Any of the makes you mention would be quite suitable. i, A.W. (Auckland): How could I at- * tach headphones to my set? A.: See reply to "Mho," given above, 2..I can receive a number of stations on two different readings, Is this, usuai? A.: Not with your type of receiver, It evidently needs realigning. ‘e C.C, (Nelson): The condensers you * mention should be .00025 mfd. and .30005 mfd., ie., 250 mmfd. and 50 mmfd. 2. I would like to wind the special ¢oil for the 55 valve. A.: We strongly advise you against doing so, as, without proper equipment, it would be almost a hopeless task to match it to the preceding coils. KR, C, (Taumarunui): An article on the ° Beverage aerial appears in this week’s issue. A. (Picton): I require a new set of * valves for my four-valve battery set, At present I am using two 609’s, a 615. and a 606. Are they of the right type? | A.: You have not stated the type of receiver you are using, so it is difficult to answer this. However, the 606 is a superpower valve, which imposes a very heavy drain on your "B" battery. 2. What Mullard type valves are suitable? A.: Three PM6D’s and one PM6 or PM256. RR A.E. (Cromwell): You cannot use * your autodyne superhet. kit for the "Sky King Six," as this set employs 4 separate oscillator. You could employ the

Feeeeeseraaerenearts SPT ecepvcrcesaseyereneareee’ information Coupon (To be used with all requests for information.) Name of set ....... eect newer ecenes Mode! sence cccccncenacnessaveseens Name sOeeeseeseressesseeseseseere Address secuoncecousccversensouass PE MOS TES Ce SS ESE RTOS SOU SESEEEESEOEETE PROP R eee e ee moe ERE EH EAMES SEASESO ESE Nom de plume ... To be kept in jnauiries Please Note:{1) Be specitic anu ortet. tabulating, if possible. (2) Write legibly and on one side of the paper (8) We do not design circuits. (4) Limit three questions unless 1/- is enclosed (5) Postal queries limit 8 questious. Iinclose stamped and addressed envelope and 1/- fee. ~~

system of biasing as used in the "Quality Six" for controlling. the -bias.on the 34 rf. and 84 intermediate valves," A’ separate "O" battery is not necessary .when using class "B." : wee R ©. (Gisborne) : I intend using a 233 * in the ‘output stages of the "Outspan Four." Would it be necessary ‘0 alter the value of the 400 ohm -potentiometer? : ‘ A.: Yes. Connect a 400 ohm resistor in series with the potentiometer, between the end now connected to earth, and earth, "CRANKY" (Feilding) : After muéh exF perimenting with short-wave coils for my set-a three-valye home-made oneI succeeded in making 4n 80-metre eoil which will work satisfactorily. I have 29 turns of 34 d.s.c. on the grid winding, and 19 turns of 34 d.s.c.-on the reaction. A.: What circuit are you-using and what type valves? Hvidently there is serious damping somewhere, as you should require nothing. like 19, turns on the re‘action winding to secure oscillation. Have you tried coupling the aerial to the’ grid coil through a .0001 mfd, condenser? Also, are you employing a low impedance detector valve? ployed. N C.. (Auckland): I have constructed * the "GSD Short-waver,"’and it brings in New Zealand amateurs quite well. . However, results on dx reception are ‘very poor.. The loud hum results. when the set is just on the point of oscillation. A.:.Try connecting a .01 mfd. fixed condenser of ‘high test. from each side of the power transformer primary to earth You- will also find that oscillation on the lower wavelengths will be much smoother if you connect a, 1 mfd. fixed condenser from the centre terminal of the unissulated electrolytic condenser to earth. Also substitute a 500,000 ohm resistor for the 1 még. at present connected to the potentiometer reaction control, to give a slightly higher detector screen voltage This "will increase oscillation, and if it does so to an undesirable extent, if ean be reduced ‘by ‘unscrewing the .00005 mfd. semi-vari-able condenser connected, bétween — the sereen and the plate of the r.f. valve. 2; Could you give me details of broadcast coils? A.: The following coils will cover the middle portion of the band: R#£ coil, aerial 25.turns, secondary 180 turns. Detector. coil, reaction 40 turns, secondary 180 turns. Wire, 30 d.s.c. If you desire to cover the complete broadcast band you will need two sets of coils, one set with about 150 turns on the secondaries, and the other with 200 turns.