WIRELESS NEWS.

Press, Volume LXIII, Issue 18906, 22 January 1927, Page 10

WIRELESS NEWS.

CRYSTALS AND CRYSTAL SETS.

(S?ECUU.T WHITIES TOE THE TEESS.)

(By "Electra/')

In the main cities where there is a "ood broadcasting station, crystal sets have come into prominence, and both in Auckland and Christchurch there are more crystal than valve set-owners. Tho crvstal set-is the simplest type of receiver known, there bein ß n 0 batteries or valves required for its operation The set consists of a tube of some sort wound with cotton-covered or enamelled wire,,necessary terminals, and a crystal detector, which is the most important part of the whole outlit Though the set is simplicity itself there are many little points which mav be watched, and if these are observed, results can be much improved. The crvstal itselt should be a good niece and should always be free from dust and grease. If a crystal is picked up in the lingers a light him of oil will often be deposited on it, and this will at once reduce its sensitive qualities. If it is necessary to remove the crystal from its holder at any time it should be lifted with a small pair of pliers or tweezers tf there is any doubt as to the cleanliness _of the crystal, take it out and give it a good washing with a tooth brush in clean, warm water. The crystal should not be held in the fingers during this operation.

A "ood -wav to preserve spare crystals is to store them in a jar of very fine, drv sand.' Before removing for use, shake the jar vigorously as this has the effect of giving the crystals a "dry wash." Dust should he kept from the 'crystal bv mounting it in a dustproof "nrtuntincr or what is generally known as a Mass-enclosed crystal detector. The adjustment of the catswhisker, which is the very fine wire that makes contact with the piece of crystal, should be very fine. Not sufficient care is being taken bv users in this point. Many of the old cWs J detectors used by the amateurs before the war had some wonderful vernier arrangements for adjusting the pressure of the contact point on the crystal. A great deal of the sensitiveness of the unit depends ; on this adjustment. . • It must be. remembered that the range of a crystal feet in the days before the valve was very considerable. We do not seem to obtain similar results on the present sets. If listeners will take the pains to make their crystal receiver a little more than 3"st a crvstal set" the e is no ™w at all wliv very good medium distance reception should not be accomplished. There are cases on record where crystal listeners have been able to receive IYA, Auckland/ and 4YA Dunedin from Christchurch. . ■ The average crystal in use to-day requires a very light contact, which means, of course, that quite a small amount of vibration, such as caused by the banging of. a..door, is sufficient :to throw it out.of adjustment. If the detector is a separate part from tno rest of the set this disadvantage can be overcome by devising a shock absorber ,on the following lines tairi a.shallowbox about.4m by 4in by 2in'or lin in depth, and after removing the lid,-fix the end of a piece oi rubber or elastic to each corner! This can best be done by .drilling a hole through the wood valid tying a knot in the elastig&pr- rubber: and then, pushing the other end through the hole from the outside. Then fix the other ends of the elastic to the comers, of the crystal base-so- as to keep tlio latter suspended midway between the sides' "of the" box. " It will be found that with the aid of this simple device a sensitive contact can be preserved for months at a time. This idea can be further irriproved by letting the detector _ m below the'level of the.tops of the sides so that the lid of the bos can be i closed without touching the detector, I which is then secure from damage in ! any form.

Making Crystals. There is a great deal of fun and useful experience to be gained from j comparing the relative merits of differ- i ent crystals and different combinations of crystal. This is a branch of wireless research which should make a very strong appeal to the amateur experimenter. .It calls for no. previous technical knowledge or experience; it is clean work; it can be carried on without causing undue interference with the reception of the ordinary broadcast programme; and, most important.of all, it involves a minimum of expense. An excellent piece of crystal can be .bought for Is 3d mounted, or 9d unmounted, and if properly cared for will last indefinitely. Then, again, a pretty fair crystal can be made by melting seven parts of lead and one part of sulphur together in -a pot arid stirring same until it hardens. Break it up into small lumps and test for sensitive points. Throw .the dud pieces away.and 'mount the other in wood, metal, or lead ready for iise. Crystals may be divided into two broad classes: those which require a metal contact and those Which give best results when brought into contact with'another : c'rystal of different composition. The best-known example of. the first-class is galena. ,This is a common ore of lead which is' found naturally in great abundance. In its natural state, however; it is not suitable for radio work, but it can be treated by a certain • process which renders it extremely sensitive and reliable. ■•-J.t can .be used with a thin brass,, copper, or silver, cat's whisker, the latter-being the best. A great number- of crystals on the market to-day with a trade ?? me nd, ' n g in -"ite," are. simply. ' 'treated" galena. •Graphite, by the, way, is capable of performing wonderful feats in combination with galena. Every experimenter who has not already done so should try using a small piece of graphite.(or soft lead pencil)-with a lump of galena. , Crystals, of the second class mentioned above are usually quite stable, owing to the fact that they require a firm contact for their operation. One of the best-known detectors of this class consists of a lump of bornite and a lump of zincite, pressed nose 'to'nose, as.it were. These..crystals should.not be handled too roughly, however, as they are both extremely brittle. Zincite and tellurium also make a good combination. Molybdenite is a crystal which is sometimes used in combination with zincite, silicon, tellurium, or graphite; but it gives best results when used with a flat 'silver springcontact.

Hertzite, neutron, R.D.Fv, Empire, and various other crystals are- all siood, and are, as a rule, all natural crvstais with the sensitive spots brought up. For a matter of 9d or Is it is quite worth while buying any new crvstnl that comes on to the market i° see if it U an improvement!'

Across the Tcs^ian. Work has been started on rhc new studios for 3LO, Melbourne. A twostorey building in the' centre of the city has been taken and when transformed will be-me of the finest studios :'n the world. ]t is proposed to have two studios, and to continue the policy of admitting the public .«a audience.

3LO arc also Dialling tests.ivitli the new Reisz microphone, which'is one of :i type recently adopted by tho 8.8.C. Its advantages are verv great. None of the hissings and blurring, inherent

•in many microphones when over-aniph-fied, are noticeable in this instrument, which gets nearer to absolute fidelity of repioduction than any other microphone so far available. Reports from the south state, that the Australian stations are very hard to get, and all New Zealand stations are fading badly, particularly 4YA, .Dunedin, while in the North Island the Australian stations are very lair for this time of the year. In Invercargill 3YA and IYA aw just about on a par for strength. Everybody is cailinE out for a new high-power station for Dunedin, and it is about time they had one, too.

It is noticed that a crystal set of English make can now be had from if low as 9s 6dat J. I. Smail. of Carey s Buildings, Colombo street. We believe that this is exceptional value. .—u Have;..you heard the SFERAVOX? U not. ask to hear one at your local dealers. A trial will'convince you that it is the most perfect loud-speaker you have heard., One style and one colour, and only ■-'..'_ •'. • ;■, £5 53 of all leading Tadio dealers.—New Zealand ■Representatives, Brown and Dureau,. Ltd., Wellington. ■—4