QUESTIONS AND ANSWERS

Radio Record, Volume X, Issue 7, 28 August 1936, Page 47

QUESTIONS AND ANSWERS

"7 HP." (ss, Waimarino) writes: * "Just to let. you know the suécess. J have had ‘with the "Selectivity Unit" as described in the last three issues of the ‘Radio Constructor'’s Guide. It’s worth its weight in gold to anyone with an uaselective set and there must be quite a few using a batlery set as I am, whe ure tired of trying to get a wave-trap that doesn’t reduce sensitivity-and Il have tried a few. The set I use is a twovalyer using detector and one audio su that with it dx is impossible until the locals have closed down. But with the unit, how’s this for dx? On Saturday, July 11, within a few miles of Lyttelton not only was I able to log and report KGMB, Honolulu, but I was able to listen to him for over an hour. Without the unit 8YA and 3¥YL both-spread all: over the band. Again at my home in Mount den, Auckland, on Saturday the 18th, using an aerial 150 feet_long and 45 feet high, I heard KSL, Salt Lake City, while 1YA and 1ZM were both working, without a trace of either of them. Also I find that it will cure my superhet-of cross modulation, being able to cut out the whistles caused by 1ZB. I built the unit on a & x 4 inch base with a 5 x 4 inch panel. I would like you to mention this unit in the ‘Record’ to let others know how good it is." "MANAPOURT (Manapouri): There is a possibility that the B_batteries are getting a bit weak and that one section is giving its voltage intermittently. If a fresh battery, in place of the block where the 224 volt tap was taken, ean be tried and does not cure the trouble, it is a case for a serviceman. " H.N." (Pipiriki): The series ar- * rangement of the Daniel cells would do quite well for the three valves, but if there should be a necessity for extra current it would be best to increase. the copper plate and if the zinc is in the form of a plate, increase it, too. If the zine is in the form of a block there is usually enough area in the shapes cast to do for these sets, The copper grows in size while the zine diminishes, . with use, " A NOTHER T.R.F" (Clyde) : The preselector unit is described in the 1936 Radio Constructor’s Guide," on page 121, and the cost of building should be little, as the only components that must ‘be bought are the two-gang condenser, a piece of former and a little wire, "A LL-WAVE" (Allanton): The twisted pair for the double doublet can be three or seven strand rubber-tovered lighting wire, which is obtainable at any

‘ electrical.contractors. The cheapest way: -to buy is by the coil of 100 yards, and . split it up among your friends, This is 2 ' ‘single wire and is easily twisted; there are twisted wires available, similar, but only the larger firms have stocks of this, . oo "BE W. NTH. AUCKLAND" (Wells- ° ford) : The German shortwave stations are usually. much louder than Daventry,. due to their greater powér for one thing, and the other bands:you mention are not So good, at their best, as the lower ones. Hence you will see that your reception :is probably normal for this tinie of.the ‘year. The British stations will be using greater power shortly, so that we should have much better reception, ‘ "TM." (Crushington): The symptoms * given by you of your set point to a faulty component, and it would be well for you to get the serviceman who i stalled it to have a look at it. The symtoms are not sufficient to tell you how to do it yourself. "J B." (Auckland) : We are afraid that * you have set yourself gq nasty little problem wishing to receive 20-metre signals with an elevated loop. The size of the loop and the turns are linked -together with the size of tuning condenser to be used. Unless the loop were tuned the response would not be too good. Ther there is the question of the feeder-line from the set to the loop, and balancing if one wishes to use the loop for directional work. Its rather too difficult for any but an experienced ‘person. "TIGMONT" (Midhurst): Hither diode will act for AVC in the 2B7, A.:That field coil seems to be too he: for our liking as its temperature is in the region of 170 degrees. However, if you can find out if that particular make runs at that temperature don’t worry further as some are constructed for those temperatures. A cooler running field would allow higher voltages on the maiv set. A.: Numbers of filter condensers sizzle when the'set is first turned on due to the high voltages until the other valves warm up and take current. "NTZ315W" (Wellington): The use of capacity coupling in the "Sky-Hawk"’ is quite feasible, but there is a better all-round performance with the inductive coupling. Selectivity and sensitivity are decidedly greater all round. .: Jhe particular transformer you have will not be successful with the sec ondary carrying current but, if the sec. ondary is left open, and the primary used tor ithe choke portion it will do excel ently. : . "¢NURIOUS" (Frankton): The various components you mention are all good but. it is not fair to ask components by different makers to work together and to expect them then to line up. and also track with the dial. Whichever components you favour, stick to the one coil kit condenser and dial that have been de signed together. The differences in the condensers call for differences in the dials, therefore the condenser. coi] an¢ (lial must go together, "wo A.: No. the sensitivity control control rhe actual sensitivity as the name impliebut a tone control conld. be fitted as you: suggest. But make the set first and see whether you need it. We don’t think you. will want it: when, you have ‘heard. the set and become used to the faithful reproduction. ._ ae

"MBs. A.M.W." (Geraldine): The difficulty you have with regard to the numbers where stations can be heard on. your set is one which a number of people have to put up with. These sets are not marked in any way which corresponds to wavelength or Kilocycles and ,__each matter of this type of set puts on numbers which unfortunately correspond with no other ‘maker. Hence, it is not possible to give a table which will correspond with even a few makes. Your set number's -for instance will not be even the same as all the other sets of the same make as your own! All the médern ‘sets, however, have éither wavelength «or kilo--eyeles marked on’ the dial and are fairly accurately calibrated, so that‘ they will always be able to be used to find stations from published lists, as they are marked . with a standard measure.

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