Questions and Answers

Radio Record, Volume VI, Issue 51, 30 June 1933, Page 27

Questions and Answers

U V.W. (Lower Hutt): Could I get * QYA and 2ZW on the speaker with & one-valve set? A.: You should be able to, but the volume would certainly not be overpowering. 2. Could T use d.c.c. wire instead of d.s.c. for winding the coils? A.: Yes, but put on two or three more turns on the secondary. 8. Where can I buy powdered sal ammoniac and manganese peroxide for making dry batteries? A.: From any chemist, or from George Wilton, 156 Willis Street, Wellington. "(N\URIOUS" (Mosgiel) : Could I use a short-wave adaptor with my receiver, and would it harm the set in any way? A.: Yes, quite easily, and it would not be at all harmful. If your set is a t.xf. model, the adaptor should be plugged inte the detector socket; if a superhet., into the second detector socket. Are there any valves with which } could obtain better results than those which were installed by the manufacturers? ‘A.: Your set is a fairly recent model and any slight improvement which migat be noticed after incorporating the new valves would not justify the cost of having the necessary alterations made. 8. The aerial I am using is 40ft. high and 140ft. long, The earth lead is 35ft. long. Could T improve on this? A.: Your aerial is rather long for the type of set you are using, and you will probably find that if you eut it down to 100ft., including lead-in. you would get better separation of stations. Your earth is rather long, though with your «et. which is probably earthed through the mains as well. no improvement woul] be noticed if it were shortened. "(\HAKRATA" (Nelson): A comprehensive article, outlining methods of minimising power interference, will be published shortly in the "Radio Record." R B. (Wellington): Could I sharpen * up the tuning of my receiver by placing a fixed condenser of .0005 mfd. capacity in the aerial? A.: Yes, a slight improvement in eelectivity would be notiecd., but a smaller value condenser should be employed, say. 0001 mfd. Your best plan would be to purchase a semi-variable | compression tyne condenser of .0001 mfd. maximum value. Adjust this for best results. 2, How ean I ent ont tramway interference? My aerial runs at right angles to the overhead and power lines. A.: Interference from the tramway system is one’ of the worst nossible forms. and we doubt very much if you eould eut it out completely. Tlowever. it can certainly be minimised by one of the methods which will be outlined in the general article on eliminating nower interference. which will appear in the "Radio Record"

shortly. [Note: As a general rule we do not encourage amateurs to make alterations to commercial a.e, receivers.] J B. (Christchurch) : I am enclosing the * circuit of a one-valve amplifier I am using at present. Could it be improve‘ on? A.: You do not state the ratio of your audio transformer. For greatest volume, this should be about 7:1. Otherwise no improvement could be effected. 2. I am using an ordinary flat type torch battery for bias. ‘Would results be

improved if I used a proper "C" battery? A.: Not if the bias voltage recommended by the makers of the valve you are using is 4} volts, for the ‘‘B" voltage employed. A Y.Z. (Matiere): Reception on my * battery set is often accompanied bya erackling which persists, though to a lesser extent, when the aerial is disconnected. At times, even when reception is quite good, it will suddenly cut off altogether. A.: Your question is not quite clear. Do you mean the set cuts off, or the noise? If the latter, then the trouble is probably due to power interference, possibly from a vacuum cleaner or some similar electrical machine. If, however, reception stops completely, it appears as though there is a break in either the primary or the secondary winding of one of the audio transformers. Are your batteries in good order? If you are using an accumulator. for "A" supply there is a possibility that sediment has collected at the bottom of the accumulator case and is partially shortcircuiting some of the plates. This would eause the crackling of which you complain. "A MRAD" (Auckland): The valves you propose using are quite suitable. However, you will need a 6-volt accumulator, not a 4-volt, as they are all G-volt valves.

A T.H. (Wellington): Could you give * me the capacity of the two ganged condenser and full particulars for winding eoils suitable for the circuit I enclose? A.: Using a two ganged condenser, .00025 mfd. per section, the following coil particulars would be suitable: Aerial eoil 20 turns, L1 95 turns, L2 95 turns, reaction 40: turns, all wound with 30 d.s.c. on l14in. diameter former. "P)1GGER" (Hamilton) : When testing my "B" batteries, the set being turned off, there is a grating noise in the speaker. Does this mean that the "A" battery is not properly out of circuit? A.: No. It is quite normal, and is due chiefly to the charges stored by the various by-pass condensers in the set. J F. (Auckland): Results from my ® crystal set used to be excellent, but during the past month volume has fallen off, and although I have tried two new crystals, no improvement results. A.: The lack of volume might be due to the headphones, for if you have dropped them, the magnetism will probably have suffered. Possibly, also, the diaphram has become rusty, which would impair sensitivity. Otherwise, the poor volume might be due to the development of high resistance joints either in the aerial and earth system, or in the set itself. : "A& JAX" (Lower Hutt): I have a detector, two audio, set and would like to incorporate a volume control, using a 25,000 ohm potentiometer I have on hand. Would this be suitable, and what would be the simplest method of connecting it up? A.: An effective volume control would be provided by connecting the slider and. one terminal to earth, and the other ter minal to the aerial terminal on the set.

Information Coupon (To be used with all requests for information.) Name of set COS OHOHSSESHOOCOHSGOSOSOE Model Foe 0S OCOOSESEADSOSESOSOSOEOE Name Fer sear eeeccoosoeOsoeoosoese Address COSFSHOSSESOSSSSSOSSOOSOOe POSS OHS ESOS SSOOSOSESIAOSOHOSSESIOSTO PSPC PSOE EHTS SSO ROSOASHOOHOSOOOOOSE Nom de plum ecvevecscccescece To be kept in subsequent Please Note:41) 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.