Questions and Answers

Radio Record, Volume II, Issue 30, 8 February 1929, Unnumbered Page

Questions and Answers

A Grating in the Speaker. .[, HAVE a three-valve set which has , developed a grating noise. I have a.new, B baftery and a wet-A battery. r ,have disconnected the aerial and earth and turned off the rheostat, but Jett the set going, and still: the noise continues. -PUZZLED.. (Christchurch), ANSWHR: There appears to be a faulty. component. Test transformer resistances, condenser, ete., by the Phone and cell method. The Ground Connection. : ‘¢¢[MPROVER" writes: Could you -tell Ine how to fix a ground wire to a ‘kerosene tin in order to make the earth deseribed in the "Radio Record" some time ago?. ANSWER: Take a kerosene tin with the: top. on. Cut a small hole in this, ‘sufficient to.allow a length of downpipe to,be pushed in. . Solder this to ‘the tin ‘in order that there might be few gaps in which the soil can creep. ‘Now bury the tin about 5 feet in the ground, leaving the dowx-pipe projecting above the ground. It is quite an easy job to solder a piece of thick stranded wire on to this pipe, and then fill the tin with water and keep it filled by means of the pipe. A Buzzing Sound Heard. KAC8 time I connect up my receiver, (writes T.8.0., Blenheim), I hear a loud, buzzing noise, which ceases when I disconnect the B, and connect it again. *ANSWHR: It is quite apparent that there is a faulty component in the set and that the buzzing represents the current bridging the gap caused by the break. When this has been bridged by the expansion of the metal, the set will work 0.K. Test all the components, particularly the transtm

former, by the ‘’phones and cell’ method, and the. trouble should -be easily located. , Audio Valve Reetifying. A L. 8. (Kilbirnie), writes stating * that he has made "Pentode’s" three-in-one set. He has been more than satisfied with the volume, but is unable to stop the valve rectifying. He has tried all the published suggestions, but has not had success. ANSWHR: The difficulty is hard to eliminate because the set-is being used so close to the station. If, as the correspondent remarks, his set is going satisfactorily, he will have to leave it at that. Reaction Condenser Useless. "PIA8MonIcs" (Levin) writes :-"I ‘have a three-valve (1-V-1 neutralised) set, and the other day I purchased a dull-emitter power valve. This inereased the volume at least 200 per cent., but now my reaction condenser is practically useless because when used over about.10 degrees" on the dial a "motor-boating" is started in the phones. Can you tell me how to rectify this?’

ANSWER: It is apparent that there is something in the set that is not functioning as it should do. Test the grid leak and all the grid returns, Try a by-pass condenser between the primary of the audio transformer and between the B positive terminals and earth. The detector voltage should be kept low, while the use of a high frequency choke between the first audio transformer and the tickler would probably clear things up. If this high frequency choke is used, a condenser should be connected between the trans- , former end of the choke and the earth. This connection is shown in an article on reaction, appearing in another part of the paper. Set Out of Neutralisation. "NGAIO" (Wellington), writes stating that he has made the Brown-ing-Drake and has been very pleased with the results, but adds:-"I started off with 15 turns on the tiekler, have reduced to 18, but still find oscillation rather fierce. One point rather. puzzles me: Sometimes the set goes into oscillation on turning the tickler. down from the right-angles position, and at others it does not oscillate on turning down (i.e, to the right), but only on turning up (to the left). Why? Sometimes it is impossible to get her out of oscillation without detuning; should I still further reduce the number of tickler turns?’ The correspondent then asks for a diagram of the condenser method of controlling reaction, This is’ given in an article appearing elsewhere in this issue. His troubles seem to be not with the number of turns:on the tickler,, which, by the way, should got be reduced too much, but that, his set requires neutralising. : Unless.the set bursts into oscillation when . the reaction knob is turned low, the'number of turns should not be reduced. Coll Specifications. . " , ». T." (St. Albans) writes asking for the particulars of the coils for "Pentode’s" three-valve set ‘deserib- |} ed in our issue of January 18, 192%.

ANSWER: The aeriai coil is spa¢ewound on‘a three-inch former with 20 g.w.g. Wire, Put.on 65 turns, and tap at the eighteenth turn, The secondary, if 20 gage wire is used, requires 53 turns, if tuning with.a 005 condenser, 68 if a 0008 condenser, and 90 if with a 00025 condenser. If 22 gauge wire is used, put on 49 turns, 68 turns, or. 85 turns, according to the. condenser used. The approximate tuning: range of the set will be from 200 metres to 550. metres. Which is Most Efficient Aerial? | G., Wellington: My present aerial * runs over the top of my house. I propose to alter it in order that I may get-more efficiency. If I were to erect an aerial with two wires: 2ft. apart, do you think this would be better? or would four wires 48ft. long be still.more efficient? ANSWER: The best. aerial will be clear of all earthed objects and about 80ft. high. If a multiple aerial is. desired, the wires should be 6ft, apart and sepatated by non-conductors, They may be brought together for the leadin, but make this as short as possible. The question of aerials was dealt with ' in our special issue of December 14,

B Battery Running Down Rapidly. P E.N., Marlborough: I am using an * American factory-built set designed for Amefican valves. I have recently changed to low consumption valves, and find that my B batteries have dropped from 40 to 20 volts in a month. What is the cause of this? ANSWHR: The particular set in question is unsuitable for any other yalve than the American valves specified, and the change to the low filament consumption valyes should -not have been made. This would account for the sudden drop in voltage, greater drain being put on the plate. At the same time, there may be a short circuit somewhere in the set. Test the by-pass condensers by. the ‘phones method, and at the same time, check over all the valves and valve sockets. It is quite probable if the correspondent uses the 201A valve instead of those he is at present using, he will have much better results. G. T.F. .(Cambridge) writes stating that he has changed the bright emitter valves used in his factory-made set, which is the same -as that of the correspondent above, to dull emitter valves, He adds: "I was told that. if the D and V dials (the rheostats controlling the filaments of the valves) were left on 100, the A battery would last longer." This is incorrect, as the lower the filaments are turned the longer the yalves will last. He rez marks that he notices no increase im volume after he has passed the_division marked 5. This indicates that. lis’ valyes require. a lower voltage , than that supplied by his accumulator Under these circumstances, if he burns his valves with the battery full he is not only lesing efficiency of tone but is burning his valves out to no pur‘pose, As remarked in the previous letter, the change to dull emitter valves, taking that these are the English or Continental valves, should not be used im this: parties lar factory-made set,

Ammonium Phosphate. _ KX ©.T., Havelock -Notth: I have been "* unable to obtain. ammonion phosphate for the trickle charger describ.by "Pentode." Where may I obtain would be able to supply it. Try Kempthorne Prosser’s, Wellington. 4-Volit Valves in 6-Volt Batteries. "[N TROUBLE," Miramar, writes :- " (1) As the 30-ohm rheostat cuts down the 6-volt current to 4 volts, does ‘it mean that if I use a 30-ohm rheostat on my circuit, I shall have only 4 volts on the filament when the rheostat is turned on full? Yes, (2) I would prefer to use a fixed resistance on the 4-volt valve as then there would be no chance of the valve being burht out if the audio rheostat was switched full on. Could an amperite be used? ANSWER: Yes. A fixed resistance@® may be used and the amperite ty would be particularly suitable, There ‘is a particular number of these for each valve, so that it will pay you to consult a reliable dealer before purchasing the particular resistance you want. (3) Is it permissible to use a -variable condenser across the primary of the aerial coil? Yes. The only difference will be to weaken. the strength. ANSWER: Any of the elty chemists:

What are Harmonies? "TF ARMONIOS," Levin: Will you tell me the cause and the number of a station has, or, in .other words, give me a general explanation? ANSWER: A harinonie is a- frequency which is a multiple of another frequency. The first frequency is called the fundamental frequency. A fre. quency twice as great is called the sec- ~ ond harmonic, one three times as great is the third harmonic, one four times" ag great ‘is called the fourth harmonie, and so on.. Starting with a fundamental frequency of 600,000 cycles or 600 kilocycles, for an example, its second harmonic would be 1,200,000 cycles or 1200 kilocyeles. Its third harmonic would be three times the fundamental, or 1800 kilocycles, the fourth harmonic ‘being four times the fundamental of 2400 kilocyeles. In broadcasting it is desired that the transmitter send out a carrier wave of a fundamental frequency only. No harmonics are desired, in fact .they. are very- harmful, since they too are transmitted and may be. received if sufficiently strong. Taking the series of harmonics of the fundamental frequency of 600 kilocycles mentioned in the foregoing paragraph, it is interesting to trace the frequencies and wavelengths of the several harmonics. The second harmonic of 1200 kilocyecles corresponds to 250 metres wavelength. ‘The third harmonic of 1800 kilocycles forms a wavelength of 166.6 metres, The fourth harmonic of 2400 kilecycles is at a’ wavelength of 125 metres, while a fifth harmonic of kilocycles' would have a wayvefength of 100 metres, In each case the pproximate wavelength is found by dividing.300,000,000 by the frequency in feyeles: or by dividing 300,000: by the frequency in kilocycles. The "Three-in-One." H4vine made up your Three-in-One set there are one or two points that I should like a little further elucida- P tion upon, They are: °

1. Using a carborundum crystal, ' would it be advantageous to use a large:ratio transformer, say 6-1, or would distortion creep in? =.=: ANSWER: Providing the curve -is. Pelatively flat the ratio may be high. 2. What are ‘the relative merits of moving tickler and throttle control. regeneration? ANSWER: Base smoother, alters timing. (See article on regeneration.) 3. Is the double grid valve suitable for use in this set , ANSWER: It would be suitable providing there was not a great deal of volume to be handled. ; My aerial is fairly proficient, but, living in an upper story I have a very long earth, about 50 feet, which increases the external resistance of the set. Still, my results have been very good. 1YA roars in on the speaker, while 1ZB, 2YA, 3YA, and 2FC have, under favourable conditions, come in with very fair ’phone strength. 4 ‘+ However, I think I could do much ‘better, for I have noticed that when I tune in a distant station-say 2YA-and turn up the filament a little, the set begins to whine, the same thing happens if I turn up the conderiser. In other words, to tune to a higher wavelength than the local the rheostat has to be turned down with a consequent loss of signal strength.. Substituting an H.I. choke for the grid leak makes no difference, ‘neither does it stop when I disconnect the aerial and earth. At present I am using a carborundum erystal without brassing battery and a "free grid," which I find gives clearer reception. Can you ‘enlighten me on this point, please?-D.J.J. ANSWER.-To overcome this difiiculty by ‘he addition of grid bias, eheck, the cickler coil. If the set osceillates at a low reading some turns can well be taken off; if at a- high, more added. Shortwave Reception. ' HAVE a locally-constructed three‘valve short-wave set, which is not going too well. On Wednesday and Thursday -night I. was listening-in to a- foreign station, PCLL, on about 20 metres. It was very mushy and distorted. I could not clear it up at all. "Allo, allo, allo," was all I could make out. I use dull emittor valves, 90 volts, B dry batteries. Is this all right, and can you’suggest something to bring -in American stations, as I liavt not heard them yet since I added this short-wave set in October last to my. possessions. I get good results with a factory-made six-valve set on the broadcast band. Could you advise me how to test audio frequency transformer? It does not seem to have much kick-NEW:> CHUM (Otago). ‘ANSWER.-Judging from the re- " ports, short-wave reception is bad just at-.present, and this-is probably your trouble, for everything you report on seems so. ‘However, as is suggested, a component may. be at fault. Test _these by the ’phones and battery method described in the Beginners’ Corner recently. ’