Questions and Answers

Radio Record, Volume V, Issue 45, 20 May 1932, Page 10

Questions and Answers

L. H. (Fairburn): I have been unsuccessful in attempting to re-neutral-ise my old neutrodyne. I covered one ot the filament terminals of the detector yalve, but could hear nothing on 1080 @ A.: It appears that you are attempting to re-neutralise the set with the detector out of action. You do not disconnect the filament supply of the detector, but start with the radio valve nearest the detector. If you cannot get a strong signal on about 1000 k,c., take one on a little lower frequency than is, K A.F. (Oamaru): The gramophone * part of my set is far too heavy on the bass, while the radio side is well balanced. How ean we cut out this bass? , A.: Use a condenser in series with one of the leads to the set. ‘The value of the condenser should be about 01 mfds. However, the pick-up you are using has rather a preponderance of bass, but the condenser should prevent much of this going through your set. If this condenser does not stop sufficient bass, use a smaller value, say, .005. C F.C. (Waipahi): What is the correct method of neutralising my four-valve battery set? A.: Wrap a piece of silk around one of the filament prongs of the r.f, valve nearest the detector, and tune in a station about the middle of the dial. Adjust the neutralising condenser until the the signals almost or totally disappear. This stage is then neutralised; repeat the procedure for the first stage. ADAPTOR (Auckland): Would a s.w. adaptor such as I have sketched work with a 6-valve commercial set ‘and bring in siw. stations on the speaker? A.: The circuit is an orthodox one. Whether it will bring in s.w. stations on the loudspeaker is difficult to say. It should. 2. What is a grid return? A.: The grid return is the connection between the grid of the valve and the filament. In your ease it goes to a 400 ohms potentiometer. 3. What is meant by "one, Stage must resonate with another stage’? A.: They must both be tuned to the same wavelength. pUzZZLED (Hamner Springs) : I have built a set from a 5-valve commercial set, and designed it to work from a d.e. eliminator, Before altering the set I had good reception and now I can get only half volume. When.a potentiometer is a quarter on the signals are weak and then on the set will only howl and squeal. Above three-quarters it is silent. A.: With such a cireuit you should use a soft detector. Try taking the grid return to the other side of the filament. Take the grid return of the first valve to "A-’ and try placing the potentiometer across the filament of the detector yalye, and bringing in the grid return to the moving arm. See some of the cireuits which were published in a special series of articles which ran in the "R.R." some time back. You may find it an improvement to employ a centre tap input push-pull transformer. AGP? (Hindon): Particulars of the coils appear to be about right for the Cossor set; we cannot say definitely ag the condenser value is not given. They would be worth trying. N=£y4 (Wellington): When I turn on the s.g. stage of my Radiogram Five I get no extra ‘A: It sounds as though you have the eonnections to the s.g. valve incorrect.

a 2 ener re semana canara If you are using the American type the grid is on the top. Otherwise it is the plate and the plate terminal becomes the Sereening grid terminal. Are you certain there is no break in the connection petwoen the screening grid and the batery? G C. (Awanui): I econstructed the Xe Daniells Cells battery, using commercial zine and sulphuric acid, but the zines burned black and the cell would not function. A.: Your sulphuric acid solution is far too strong. Out it down by half, and then try. 2. My four-valve set uses up any kind of battery in four months, irrespective of the valves used. A.; You probably use your set a good deal, With a four-valve set you should get at least six months from a sét of batteries if they are used on an average three or four hours a day. A SNW (Westport): How can I erect sal? a cheap and eflicient inside aerA.: Sling a couple of wires spaced from 4-6 teet in the attic and bring down a single lead-in to your set, DJSSATISFIED ( =): Why have three 224 valves blown out in six months in my commercial radio? A.: In all probability the filament winding is of too high a voltage. Have it tested. W.A. (Waikanae): How -.do you ° work out the coil construction chart on page 145 of the 1932 "Radio Guide" ? A.: The first operation is done with the vertical lines EH, F, and G. ‘The ruler is placed upon’ the value of the condenser to be used, indicated at "G", and upon the maximum wavelength to be tuned in on "FE." It then touches a point on "HW." From this point the straight edge is laid across "D," "C," and "A" so that it cuts "A" at the numeral indicating the diameter of the former. Mark where this straight edge (Continued on page 21.)

abahinge Information Coupon (To be used with all requests for’ information.) Name of set dseecovaceareees Number of valves PYTTITITTTT TTT Name Fre emcee ee oeeeeeeeeseseere: Address sec eevesenescceeseenesnesr: TSS SSSESEHOFSOESSESESOSESSESEHSBO OS SSH THO H He eee EROS HEH SSOSSESSSEROESOES! Nom (le Plume ..secceesccccuvece To be kept in subsequent inquiries Date eoeecwe + evcccaccssess Please Note:(1) Be specific and brief, tabulating, if possible, (2) Write legibly, and on one side of the paper. (3) We do not design circuits, but accept suggestions for feature articles

Questions and Answers | (Continued from page 10.) crosses the base line. Place .the straight edge on "B" at the gauge of wire to be used.. The figures on the left denote the number of turns to the inch for this particular gauge of ‘wire. The straight edge is taken through the mark on the base line and at "CO" indicates the number of turns and at "D" the length of the winding in inches. This will tell you only the details of the seeondary winding. The primary and tickler have to be,computed by other methods. For an aerial coil the primary can usually be considered to be one third wf the secondary and without any, further information the same is true for the primary when used in a split primary circuit or other orthodox circuit with 2 triode valve. The tickler depends upon the size of the condenser, but, for a .0002, is about the same size as the primary. Smaller and larger | sizes require more or less turns respectively. . 2 and S21 are suitable for the "DX Two."