Questions and Answers

Radio Record, Volume V, Issue 39, 8 April 1932, Page 11

Questions and Answers

"FT CONOMY" (Ashburton).-I have a three-valve set, but cannot get Dunedin or any other station below 2YA’s frequency; If I raise the detector voltage ito 50 volts they can be heard at R2. There are 55 turns on the primary, 60-on the secondary, and 40 on the tickler. A.: There are too many turns on the primary. Try bringing it in to the 18th turn from the bottom of the secondary. Does the set oscillate? I£ not, try reversing the tickler, Whereaouts ‘does Wellington come in on your dial? You may have too many turns on the coil. 'These and other things should have been stated if we are to diagnose accurately your ease, "FX ADIO" (Waipawa.)-Is a stage of ‘ rf. sereen-grid, detector, followed by one audio stage (pentode) superior to the usual sereen-grid,’ ordinary detector, and two audio? J A.: It is doubtful. We think the three valves employing the sereen-grid ‘with the pentode would just about as powerful as the four-valve set. _ 2,'In some meters it says "resistance 200 phme per volt.’ What is meant by 12 "4.: It means ‘that the total resistance of'.the meter is the maximum voltage multiplied by the number of ohms per yolt. 3. What is the resistance per volt of a voltmeter for reading "B’? A.:'To get accurate reading you should have 1000 ohms per yolt. However, 250 will give'you a fairly accurate result, "PIO GRANDE" (Auckland): Yes; if you are getting a great deal of interference jn your existing aerial, try reducing it, Another good 'plan is to shield the lead-in, using special armoured cable. 2. Sometimes I hear quite a number of stations between 3 and 5 a.m., but have not ‘heard any calls. What would

be a suitable book for me to get for these call numbers? A.: These ‘are probably Europeans, an excellent list of which appears in the 1932 "Radio Guide," which will be on sale shortly. 8. No, do not pour oil down the earth pipe. If you want to make the earth good, douse ‘it occasionally with salt water. Frequently the earth on an a.¢c, set makes very little difference. "9 4. W" (Oamaru) : Yes, you can use the "Sparrow Hawk" one‘as an adaptor for an S-valvye a.c. set, by using the detector valve of the broadcast set and running it from the power-pack. See the 1931 "Radio Guide" for a full explanation of how the "Sparrow Hawk One" can be used as a shortwave adaptor. 2. Why do the "dead spots" on the dial of the "Differentfal One" shift and ‘disappear on different days? A.: It is probably due to dampness ‘in the air affecting either the choke or the aerial, "BEGINNER" (Auckland), — You would probably get better ‘results by increasing your aerial as suggested. ou can cut down the interference from 1YA by using either a wavetrap or a band-pags filter. Wavetraps have been frequently described in the "R.R.," and a band-pass filter will appear ‘in the 1952 "Radio Guide." H K.S. (Auckland).-The "Knife Bdge * Rejector" could be used satisfactorily on your set, although the one in it at present is of the "Knife Hdge" type. A still better plan would be to use a bandpass filter, such as is described in the 1932 "Radio Guide." "A RIL" (Dunedin). — Body effect quite frequently improves signal strength, and it appears to be doing so in your ease. Yes; you could do away with the potentiometer grid return, but you would probably have less smooth reaction. We are glad to know you have secured good results on the "Sparrow Hawk One." It is a good set. "DOWERTONE" (Dunedin).Yes, in the "R.R." March 8, 1929, we described very fully the construction details of a moving coil loudspeaker. These numbers, unfortunately, are sold out completely. It is possible, though we are not making any promises, that constructional details of such a speaker will be given in the "Radio Times." EF G. (Timaru).-What are the details * of s.w. coils for the "Cossor Melody Three"? A.: The s.w. coils are wound on formers identical with those used on the broad-~ east band. Winding of the rf. coil is started from the plate pin. A tap is taken re . at first turn to the filament pin

(looking down on the former with plate pin nearest), and the 4th turn is taken to the left filament pin. _Windings are spaced 8-8in. The grid coil is started at G, and P, which are shorted on the coil. Three turns spaced 3-8in. are placed on, a tap beingtaken to the right filament pin. Then four further turns, close wound, are put on, the end being ‘taken to the other filament pip. " TAOKO" (Otahuhu): Theoretically your 50 ampere hour accumulator can go up to 5 amps charge, but it is better to keep it under this. Really, for safe working 3 amps should be employed. It should not be run at a temperature of 100 degrees. Write Philips Lamps, Ltd., Wellington, for literature on their 80038 "B. and ©." eliminator. This will tell you how you can calculate the yoltage for different loads, Deva (Rotorua Line): Yes, the efficiency of your aerial is to a certain extent offset by the proximity of your roof. ; 2. If your set is designed for 220 volis, and you are putting it on 230, you are not doing a considerable amount of harm. CREO C SSC CC CCST

All the voltages are about 5 per centy high, but this is not particularly serioua, , R. H.R, (Lower Hutt): Lucky maa,’ * Yes, the broadcast coils for thé "Round the World Three" will be quite suitable for Hngland, and the set will be quite satisfactory for British conditions, You will have to use a loading coil to get the long-wave'station, Better wait until you get there before you make your load» ing coils, however, as the English teche nical publications will be able to telf you more about the reception of thosé long-wave stations than we can. . " ENT" (Dunedin): ‘Your short aerial is not very short. You should reduce it much below 50 feet if you desire really satisfactory selectivity. XI4NW (Hokitika): The elaim sounds rather extravagant, but can have nothing to say about it un we have either seen or tested it. "NEw CHUM" (Christchurch): Sx cording to the regulations, you must use at least 7/22 gauge wire for tl lead~in. Wnamelled would be quite factory, as this size in rubber covered would be expensive and weighty. An insulated wire will bring in quite as much noise ag an uninsulated one, Probably you are thinking of an armoured cable. SOOO OOK IO KOK KKK KKK