ANSWERS TO CORRESPONDENTS

Radio Record, Volume I, Issue 27, 20 January 1928, Page 12

ANSWERS TO CORRESPONDENTS

CRYSTAL QUERIES.

W.G. (Wellington).-For local recep tion only, space-winding is not very important, but for distance-getting and selectivity it is of value. Any motorcar trimmer will supply a piece of celluloid for a few pence. The cement is made by dissolving chips of celluloid in liquid acetone, obtained from the chemist’s. In crystal double-de-tector circuits the two crystals should be as mucli alike as possible, In diagram No. 8 the 001 fixed condenser is probably not essential. A correspondent at Paraparaumu gets Australian stations faintly upon crystal and two amplifying stages, and wishes to know how the strength of signals may be strengthened. Probably the audio amplifier could be improved by increasing plate voltages and putting a power-valve in the last stage, but the time appears opportune for a valve detector to take the place of the crystal, or the addition of the first two stages of Browuing-Drake to make it a real set. It is possible to add an R.F, stage before the crystal, but the better way is as already mentioned. E.T. (Auckland) wishes to know if a stage of R.F. can be added to crystal and two audio stages. It is quite feasible, but not very widely adopted in New Zealand, as more volume is usually obtained with a valve detector in place of the crystal, and the R.F, valve can be added at the same time or later, The detector would work off the same batteries as the audio, (Continued Next Page.)

ANSWERS TO CORRESPONDENTS ) (Continued from Page 12.) DANIEL CELLS. One or two readers appear to have placed too much sulphuric acid in their gravity type cells, so that action has been rather violent. The original directions say "not more than one of acid to four of water," and the amount of acid may he considerably less than this, as violent action is to be avoided. The acid is only tc commence the production of zine shate solution, which rises to the +t of the liquid. and forms a distinct layer, in which the zinc must he, It is this double layer of solutions that enables the porous pot to be dispensed with. The cells will probably give full voltage when settled down. 112:VOLT B BATTERY.

"Radio" (Auckland).-You appear to have made your plates before getting the tubes, but no harm is done, provided there is sufficient space for a strip of celluloid between the pair of plates. Bv sorting the plates you will probably he able to put most of the wide ones into the wide tubes. If a few are too wide to go in, bend them slightly down the centre to suit the curve of the tube. Tuhes 1 1-8in. diameter are not usually obtainable in New Zealand. You will find most working dimensions stated exactly where necessary. The article you mention is to appear shortly. A chemical rectifier is not recommended for charging this batterv. A valve rectifier is far more reliable, and is recommended. If a chemical charger goes wrong it may ruin the battery, but a valve charger can do no harm. Ordinary insulated wire can be used in the bat tery, but enamelled is best, as the acid spray during charging soon rots cotton or similar covering.