Questions and Answers

Radio Record, Volume VI, Issue 8, 2 September 1932, Page 11

Questions and Answers

L G.Y. (Auckland): Could I use the * "Neutron Four" as an a.c. set? A.t You could do, but it is designed as a battery set. Tf you wish to conStruct an a.c. set why mot build up one of the many which are being described in the "Radio Times’?. You would get far more satisfaction. ‘The valves for the "Neutron Four" would be three 227’s and a 171 or its equivalent, but such a set would be really old-fashioned. ‘You could use the "Neutton Four" as a battery set and supply the last -valve with Sc usihg such a valve as PM4 or PM 54, P W:S. (Hamilton) : One would expect © difference -between the "Radio Guide" and the "Radio Call. Book" with respect to station particulars, as many of these have changed since the former was published, oo ‘ R B. (Birkdale): When I remove the * earth wire from my set reception is better, and if I plug the éarth wire into the aerial terminal it is the same as with’ the aerial. -By connecting the earth the aerial reception is doubled. A.: Quite possibly your aerial and eatth terminals have "been reversed in the process of thanufactute. © However, if this is not the case, you are not doing any harm by reversing them. 2. The volume is enormously increased when the earth is removed from an eightvalve battery set, but when: an electric light is switched on the volume from the spetiker was terrific. A.: By removing your earth you are working your sét closer_to oscillation, but we cannot explain why it should be terrific when. an electrie light is turned on. It may be due tg faulty electric wiring, but that is very doubtful. A, @B. (Christehurch) : I had an aerial * 15 feet high and about 120 feet long. Reception was good, though I picked up a lot of noise. .I erected a shorter aerial, but I can heat 8YA while listening to 3ZC. The trouble does not occur when listening on a long aerial, A.: It is usual that the. shorter the aetial the more selective is the set. Your best. plan to separate the two stations would be to use a wavetrap or a pre set condenser, 2. Will salt improve the earth system when fe ground js sandy and dry? .: Yes. | 21 Mo (Christehurch) ; T have had the "Sparrow Hawk" going for 10 days. atid although excellent results have been had on the breadeast and the 80 metres

te coils, the 40 and 20 metre coils are dis‘Appointing. . : "Av: If the set will not try several more turns on the reaction wiiding, but you seem to be doing quite well in getting the stations you have, Tuning on these bands needs much practice, You may get better results by experimenting with potentiometer grid retufn in order to get a finer control of reaction, This possibly wotld do away with the hand capacity with which you appear to be troubled. 2. I tried to transformer, couple, the "Sparrow Hawk" into the grid circuit of a detector valve on an a.c. set, but all I could get was a hum. ; A.: The method of the "Sparrow Hawk" one to an a.c, set was Shown in the "Radio Guide." You appear to be going about things the wrong way. 7UEW (Papakura): What are the filament voltages and current. requirements of 2A A.: We have not heard of the valve. 2. What would be the voltage drop in a 280 valve working at 400 volts o each plate, at a current of 7) milliamps?. A.: About 20 volts, which would’ be made up bya 4 mfds. condenser next the rectifier. You are asking for trouble by working an 80 valve at that point. KENT (Christchurch): Will two aerials separated by a 8ft. length of. wood and running at roughly the described angle result in interference? The aerials are On the same mast and ruh to two different sets. A.: It is possible that interference will be caused between the two. How-. ever, with the very stable receivers of to-day it is unlikely that severe interference would take place. . 2. What type of aerial would you ree commend for my set A.: No greater than 80 or 90 feet overall, the aerial to be of the "L" type. C J.C. (Hastbourne): Would you give. * me particulars of the "Night Owl" three-valye short-wave set, as 1 cannot obtain the back number of the "Radio Record’’? A.: We could not re-describe it here, but a good short-wave set has been promised for the "Radio Times." 3. Where can I get a blue-print of a short-wave set? It must be all-electric. A.: We do not know about a blueprint, but a full description of an allelectric short-wave set will probably ap pear in next month’s "Radio Times," "EF AM" (West Coast): What are the American Philips’ canipalent of. the following Mazda yalves: HL2, L2, P2202 A.: A215, A209, B205. 2. Would my short-wave three-valver be as good as the "Differential Three’? , A.: We have not tried the one you have in mind, so cannot make a comparison. Ww H. (Gisborne): I have a PMbX as * first audio and a PM6 in the last stage. Would 2 PM6’s be better? A.: No, PM6 is 9 power valve and must be used only as such. 2. What screen-grid six volt battery valve do you suggest for the "Kestrel Three’? I’ prefer Mullard valves. 2. Which of the following is the true shape of the screening box for the "Kestrel Three’? A.: "A," with the rear of the set open. [*X56HB (Hastings) : What number of turns are required for broadcast coils of the "Kestrel Three," using 13in. former, 26 enamelied wire, and .0001 eondensers? A.: You will require two coils, one with 170 turns of 80 gauge enamelled wire and the other with 250 turns of the. same gauge enamelled wire. It is not a prac

Information Coupon (To be used with all requests for information.) nie ot set SeeeSPvscerssredovbsves Model PHoeeoesccotooeceseosseoveNey | Name CeCe wpeeeesecenevccecsressas Addtess PasouCooevvactescoeecooess £294600000006060000000064 0004000000008 se eebeveesevsrsvoccscousganvceouebons Norm de plum PHO Seerenbewk To be kept in Please Note :- (1) Be specific and 2 briety tabu: tating, it (2) Writ fe legi ly and on one sidé of the pape (8) We do Gesign circuits. (4) Limit three questions. unless 1/+ is enclosed. (5) Postal ‘queries limit three questions. Enclose stamped envelope and 1/- fee, ~

ttieable proposition to make broadeast coils on such a small former and with such a ‘small condenser. It is far better to use a larger condenser and have in. series with it for shortwave, a fixed condenser, such as was recently described for the "Kestrel Three." Full particulars of all coils were published in "Questions and Answers" in radio. ad A BERDONIAN" (Wellington) : I have built a three-valve short-wave set ttaken from the "Radio Guide," 1929, and am using a pentode which ‘requires a lot of current. What other would he suitable? A.: In the Osram series, PT2. 2. Can I have wound suitable coils for broadcast fitted into valve bases? Aj: Yes. Use valve base extension coils, wind on 180 turns of 30 gauge nelled ‘wire for the secondaries, and r the tickler 60 turns of the same gauge.

2. I have beet told that by having ‘my 80 ampere hour battery rebuilt-into- an 80 amp. hour battery that. four-volt valves: wil have to. be replaced by six volts. Is is so? "A.: Not’ unless the voltage is changed. Increasing the. capacity does not affect the valves in any way. ORTHERNER" (Ngaio).-I canoe separate 2YA and 2ZW. I intend to incorporate a band-pass filter to the "Radiogram Five." Is my sketch correct? A.: For a capacity coupled band-pass » filter your sketch is correct, except that you thave connected the end of the. first tuning coil: with earth, This spoils the band~ "pass effect. A better band-pass filter be such as deseribed for. the "Link Three" in this month’s ‘"Radis Times," which we strongly advise you. to eonsult. The coils really need shielding

each with .a-can, the diameter of which should be twice the diameter of the coils, 2, Would it be advisable to shield each variable condenser? A.: Such is preferable for best results. "A DAPTER" (Hastings).-I cannot get / 4% the "Sparrow Hawk" adapter dein the "Radio Guide" to work on a five-valve battery: set. :. Try reversing the connections: to the tickler coil, iz, "C"’ and filament. Try the effect. of a midget condenser in series with the aerial, Lastly, wind extra turms. on the tickler coil, The reaction coil is rather small, and you require a large number of turns, "RUNG" (Arohina): I am using: the "Outspan Five," having used 2in. coils in. place'of the 14, but I cannot get the set out of oscillation. The trimming condenser also ‘acts as. a‘ reaction ‘condenser.. The coil is: situated over the top of the grid: Jeak and very close to . the detector valve. ° * A.3 If you are using 2in. coils, the diameter’ of the shield cans should be 4 inches, and it would have: been better ‘had you used the size stipulated. You have. eyidently far too many turns .on the detector valve. Is each stage properly decoupled, e.g., either a resistance or a choke and by-pass condenser used in the lead, particularly in the screen-grid lead, Examine the method of decoupling used in the "Link Three" in this month’s "Radio, Times" and you will get- some idea of the method of breaking a resist.anee and using a by-pass condenser, A «different r.f. choke may also make the | set more workable. It is unlikely that the grid leak is in any way affecting the set. Qvox (Auckland): What information ©, must. I supply when .applying for Q.8.L. cards? : A.: A typical report is made out in -this.month’s "Radio Times." _ 2. In estimating the type of set with "respect to the valves, is the rectifier included as a valve? . ‘A.: In modern terminology it is usual to include the rectifier, and we think in replying to most stations if you did this they would understand. "ONT MITTER" (Marton): In what issue . is the description of the broadcast eoils of the. "Night Owl Three"? "Av: December 18, 1931. 2. Is it a good receiver for an amateur transmitter to use for the reception of shortwave amateurs? . Av: An excellent receiver. . Would a stage of screen grid ahead of the detector make the eircuit more ef- . ficient?-Yes, but the three-valve set should be all you need to start with. 95MC (Picton): I cannot get Dunedin, . as my set will not. tune as low as that. ‘A.: To bring in Dunedin shunt a 0001 condenser across your main tuning condensers. It will be necessary to have one across each .condenser.

— J C. (Dunedin).-Will the powerpack * in the 1931 "Radio Guide" be suitable for the a.c, "Super Six," using three 227’s, two 224’s, and one 247 output? -_ A.: Yes, if you have sufficient windings to supply all these currents. You will need three separate windings of 18-gauge wire. 2. Where can I obtain a circuit of the ‘ac. "Super Six’? -A.: We haye not brought out the ac. version of this, and cannot supply one. Would an output filter do instead of the output. transformer for the pentode? A.: Yes, providing the filter is tapped to match the :valve The correspondent adds:: "I have had the battery operated "Super Six" for about seven months now, * and everyone.is .delighted with it, as .it has .given -every satisfaction’ both on the medium and shortwaves, Now, I wish to build an a.e: "Super Six." I find that a shortwave coupling.coil works much bet- | ter than a small frame aerial, and I have | given.o diagram of same if you wish tosend it to any of your readers. Specifieations, are. for: a .24in, former, .5 -turns |

from 1-to 3, 5 turns from 3-2, 22 dic.e. with a..0001 condenser between 1 aud © half-way up to 8, with 4 feet of wire for | an inside aerial, ~