ANSWERS TO CORRESPONDENTS

Radio Record, Volume I, Issue 19, 25 November 1927, Page 12

ANSWERS TO CORRESPONDENTS

BROWNING-DRABI. B.1). (Stratford) has built. the 4-valve srowning-Drake, but gets weak volume on distance. Departures from specifications are as follow :-~lwo 6 to 1 transformers, No. 1 mfd. fixed condenser (presumably across speaker aud filter choke), no sctries condenser in aerial circuit, and ro condenser ¢cross primary of first transformer, Your bought coils are a good make, but an AVS Verrauti is recommended tor second audio, Put in the missing parts amd see what happens, Power-house Interference. J.W. (Reefton) is sitnated near an electric power-house, interference from which prevents reception during daytime. A method of reducing the interfererce is asked for. ‘This matter was recently dealt with in ibis column, The most effective way is te approach the power-house management, and for the good of listeners in the locality get them to suitably place large capacity fixed condensers in order to reduce sparking at the brushes of their imachines. Unsatisfactory Set.

"Worried" (Glen Eden): Your letter does not state what circuit is in use. The original dealer should put the set into workiug order, and it has complieated matters by approaching auother on the question, ‘The order of battery terminals would not matter if each one was marked correctly. Distortion on increasing volume is probably caused by sinall audio trausformers. Crystal Amplifier. "New Chum" (Wellington) has made up carborundum crystal and one amplifier using grid bias. A disc cone speaker is employed, but deep notes blast badly, though results in other respects are good. ‘The cone speaker wonld reproduce bass notes, so the inference is that the audio transformer is not of sufficiently good quality to pass them along. If you have no fixed condenscr avross speaker, try one of .001 mfd. and another the same acruss priwary of transformer, Conyerting Transformer to Choke. C.D. (Manunui): As you do not give size of transformer, order ounces of 86’s enamelled wire, of which somg¢ should be left over. The lamination should be reassembled so that the join all come together, and at the two points where the outside arins meet piece of paper is inserted and the ends

are tema ee ee we pressed against while the whole is olted together. Battery Charging. | E.K.W. (Pateal: The opinion you have atrived at regarding chemical rec-tifiers--that they are at the best only an expedient-is quite correct, ‘They are used for economy of first cost, but often turn out dearest in the end, and give their owner a good deal of anxiety whilst they are running. Valve rectification is always safe and _ reliable. The transformer described in the 1 eliminator cau be differently wound to suit several purposes--experimental low voltage, or charging A or B bat‘teries, P.M.4’s would not pass enough current to charge a B battery quickly unless of sinall capacity. Good dou-ble-wave rectifier valves for the purpose can now be obtained for 17s. 6d. each,

ae ‘Aerial’? (Wellington).-The exact length of aerial is not at all critical, and as you have 100 fcet double wire, you should get good results. ‘Lhe want of selectivity complained of will be best remedied by writing to the people responsible for the circuit, There has not been inuch static lately, so that what you complain of may be caused by waning dry B batteries. A simple wave-trap already deseribed in the "Record" will improve matters. Neutralising Set. M.M. (Napier.) .-You have misread the instructions on neutralisation, as it is the neutralising condenser that is to be turned until signals are at & minimum whilst the R.F. filament is tntned off. Neutralisation must be carried out on a station that comes im with plenty of volume. oo,