QUESTIONS AND ANSWERS

Radio Record, Volume VIII, Issue 41, 19 April 1935, Page 47

QUESTIONS AND ANSWERS

oe ee eee 6. (Blenheim): Where could I obtain details of a modern battery set, taking not more than .5 amp. filament current? A.: The "Simplex Superhet Four," described in the September, 1934, "Radio Times," is an excellent little set which would suit your requirements admirably, The set uses four valves, 1A6 pentagrid converter, 34 I.F. amplifier, a 32 leaky grid detector and a PM22A output pentode. The total filament drain is .388 amp., "B" battery drain approximately 14 mils. Full instructions for building this receiver are contained in the descriptive article. I£ you would prefer a t.r.f. type of set, you would find the "1935 Birthday Five," to be described in the April issue of the "Radio Times," gives excellent results, F,)-4. (Hamilton): A single-valve short-wave converter using the AK1 octode will be described in the May issue of the "Radio Times." FAB. (Hllerslie): Where could I obtain a good circuit diagram of a one or two-valve portable set? A.: "The Trampers One," described in the January, 1934, "Radio Times," would: suit your needs, W. (Lower Hutt): The "Short- * wave Club Two," described in the 1934 "Radio Guide,’ is one of the most efficient two-valve short-wavers that has yet been described. It uses a screen-grid detector and pentode audio valve. AME. (Wellington) : I built up the a.c. screen-grid superhet converter described in the 1981 "Radio Guide," and it functions perfectly, GSD and European stations coming in very UBU EU EUBU BUREN i] RIMM B IMBIBE FE

clearly and loudly. I find, however, that as there is no "lift" in the converter I have to turn up the volume control of the broadcast set,- with the result that reception is a little on the noisy side. Could I-add an r.f. stage and use a 2A7 in place of the 224 and 227? A.: Your simplest plan, which would avoid introducing another tuned circuit, would be to add a 58 if. amplifier. It will be a matter of experiment to determine whether your present coils would be suitable when using a 2A7°pentagrid converter. A simple but highly efficient converter using the AK1 octode will be described in next month’s "Radio Times," and you might be able to use this circuit. 2: Iam planning to build a receiver using an r.f. and detector stage, with reaction, using a two-ganged tuning condenser Wowever, will not the addition of reaction upset the tuning? I intend to wind my own coils,’ A.: The effect.of the reaction winding on the inductance of the detector secondary can be largely nullified by putting several turns less on the latter than on the r.f. secondary. In this way quite good tracking can be obtained. Of course, if you wish to obtain the utmost in efficiency, it would be a simple matter to connect a fiveplate midget trimmer across the detector section of the gang. 3.: In several. of the sets described in the 1984 "Radio Guide," instructions are given-for using one or two-turns at the lower end of the secondary for reaction. -Would this suit my purpose, and -would I still be able to gang the two tuning condensers? A.: Yes, this is known as electroncoupled regeneration, and by using it you will obtain very good tracking. The cathode tap should be taken off the grid winding at a point approximately one-third to one-quater of the winding length away from the ground end. L W: (Wanganui): Judging from * your letter, the new 226 to which you. refer is defective, and should be subject to replacement. : "GRANDMA" (Kaiwaka): Your set is evidently an old model, and is not very selective. Re-alignment may effect an improvement, but this is doubtful. About the only ways in which selectivity could be improved are by using an aerial tuner or wavetrap, or by taking some turns off all the primaries on the r.f. coils. L T. (Invercargill) : Is there any way ° of determining the capacity of a two and a three-gang condenser? A.: The capacity varies appreciably with the size, number and spacing of the plates. Any radio dealer would no doubt be able to give you the capacity just by examining the condenser. 2.: I am enclosing a circuit diagram of a erystal set; is there any way of improving it? . A.: Yes, by tuning the coil with a variable condenser of from .00085 to .0005mfd, capacity, depending on the number of turns, gauge of wire. and diameter of former used. .

"COMET" (Kaipara Flats): Would it be possible to build the "Comet Superhet Five" described in the November "Radio Times" to operate from an auto "B" eliminator? A.: This could be done quite easily by using 6.3 volts equivalents of the valves specified. The "Motex Five," described in the August, 1984,- "Radio Times," was a set of this kind, and you could. obtain some useful hints by studying the diagrams and descriptions of this set. "Nicer AND DAY" (Temuka): Your receiver is fundamentally an unselective type. To improve the selectivity, you could either use a single or double wave-trap to cut out any unwanted stations, or you could use an aerial tuner, ‘O G." (Timaru): My set fades out * intermittently, but by placing my finger very lightly on-one of the valves it commences operating again. I have had the valves tested, and have examined the socket for the possibil(Continued on page 49.)

te St) HEE AUD SUE UTE GUE OUT O00 TUE GEE SUP TTT TEE ULE Pt HE ETE EU UTE ETE GP ETT GPE Eee OD | Information Coupon (To be used with all requests for information. ) Name of set Se eeeecesevesanesecseoees Model Foe scewes secrescnocececeeseeee Name A measOeeoasarecooesseoeeseeese Address Se eccoeeseeeeessoveosnessecese saccecseveccacsccccnscsceseseseaeseees CeeOeS OSS S CLOSES EEOSSOHESSCEROSOSEECY Nom de plume Sooo ees eenseseeesesess To be kept in subsequent inquiries, Please Note:(1) Be specific and brief, 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 3 questions. Wnclose stamped and addressed envelope and 1/- fee, BIEL WMATA AT TEE OTTO OE ETE EE Or

Questions and Answers (Continued from page 47.)

ity of a pin not making good contact ov for a badly soldered connection, but have found nothing wrong. What could cause the trouble? A.: If you are positive that the valve socket and the connections soldered to it are in good order, then probably the valve is at fault. The heater ov filament might be sagging on to one of the other elements. Since this type of fault does not always show up in a valve tester, your best plan would be to borrow another valve of similar type and see whether the fault recurs. "VAL" (Auckland): I built up the "DX Four" described in the "Times" some two years ago; it has given very good results till several months ago, when it ceased to oscillate except on rare occasions. I can still pick up 2YA and 3YA but no other stations, with the exception of the. locals. The valves ure about two years old. The 280 has been tested and is in good order, but the other valves have not been checked over. A.: This is evidently, the _trouble- _ eS

the other valves need replacing. In a. small set such as yours there is only a light load on the 80, and this valve could easily outlast the others. "DHONES" (Balciutha): I do not know much about radio sets, but would like to connect a pair of headphones to my seven-valve dual-wave a.c. receiver. How could I do it? A.: If your knowledge of radio is limited, we certainly do not advise you to interfere with the wiring of your set. Apart from the likelihood of your getting some very unpleasant shocks, the chances are that you would put the set out of action altogether. "DIBA" (Hauraki Plains): If by "interference-reducer" you mean the static filter described on page 119 of last year’s "Guide." then 26 gauge enamelled wire is far too heavy to use-it would make a very bulky coil. Also, the specified gauge of wire for the line filter described in the "Limes" should be adhered to, as the d.c. resistance of the wire should be kept as.low as possible. F. (Otago Central): You may be * able to obtain a dial calibrated in kilocycles from the agents for your set. However, it is very doubtful whe- ther the readings would be correct. "PICK-UP" (Timaru): How could I fit a gramophone pick-up to my eight-valve a.c. receiver? A.: We have been unable to locate the circuit your set uses, so are afraid we cannot help you much. However, if your sét uses one of the duo-diodes -either a 55, 2A6 or 2B7-as second detector, then remove the cap from the top of this valve and connect the pick-up between these two points.