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KF5JRV > TECH 11.01.17 14:17l 42 Lines 4935 Bytes #999 (0) @ WW
BID : 8658_KF5JRV
Read: GUEST
Subj: Xtal Detectors
Path: IW8PGT<IR2UBX<IZ3LSV<IK6ZDE<F1OYP<KQ0I<KE0GB<N0KFQ<KF5JRV
Sent: 170111/1215Z 8658@KF5JRV.#NWAR.AR.USA.NA BPQK6.0.13
A wide variety of different types of material were used in the heyday of the crystal radio set. Each type had slightly different properties and they each had their own following of people who supported them as the optimum type.
The different properties of the different types of crystal used in the cat's whisker detectors enabled them to be used in different ways.
Most of the substances used in the crystal detectors were either sulphide or oxides they would have been semiconductors, although they would not have been widely classified as such.
Different crystal types
There was an interesting variety of different types of crystals used in cat's whisker crystal detectors:
Galena: Galena was the most widely used mineral in crystal detectors at the time. It was said to have "well defined" rectifying properties and it "affords reception of very great tonal quality." Crystal detectors made from galena were cheap as a result of the plentiful supply of the raw mineral.
Galena is a form of lead sulphide and has the formula PbS. The material for the cat's whisker detectors was mined in various parts of the world, but supplies in the 1920s for radios generally came from Southern France, in the Andalusian area of Spain, and in Mexico. A couple of mines in England also supplied the burgeoning radio or wireless industry.
For general use, it was found that a galena crystal with a moderately fine cat's whisker contact produced good results.
Zincite: This was another popular form of crystal for radio detectors.
Synthetic zincite: As a result of the scarcity of the naturally occurring zincite, it was also produced artificially. It was produced by fusing ordinary white zinc oxide at high temperature and then allowing it to cool slowly. It then formed hard yellow lumps of the mineral. In this form it was marketed as "Synthetic yellow oxide," "Gilvium," "Azinite," and a number of other trade names.
Bornite or copper pyrites: These material are sulphides of copper. Bornite has an iridescent appearance. These crystals worked well as combination crystals in conjunction with zincite. It was also found that copper pyrites worked well with a tellurium contacts.
Iron pyrites: Iron pyrites is a very common mineral basically it is iron sulphide and often referred to as "fools gold" on account of its looks. However the exact forms of iron pyrites that can be used in radio crystal detectors are not common otherwise it would have proved to be a very serious rival to galena in view of its properties and performance. It was found that it was able to provide an almost uniform performance over the whole of its surface and it could withstand the effects of heat reasonably well. It was also found that it would retain its sensitivity for a much longer period than galena. In addition to this it provided reception with a good tonal purity.
Silicon : Although silicon is extremely widely used in modern semiconductor technology, during the 1920s it was rarely used. Initially it experienced some popularity, but this waned. Synthetically made silicon was used, and it was found it performed best with a fine wire of brass or phosphor bronze to make the point contact.
Tellurium: Tellurium, Te is an element having an atomic number of 52. It is a brittle, mildly toxic, rare, silver-white metalloid (i.e. half way between a metal and non-metal) which looks similar to tin. It is only occasionally found in native form, as elemental crystals.
As a crystal radio detector it gave excellent results when used with zincite, especially zincite in its synthetically produced form, although it worked well with other crystals including silicon and galena as well as copper and iron pyrites.
Molybdenite : This is a naturally occurring form of the sulphide of molybdenum. It was never widely used because it required the construction of a special assembly for its use, although what were termed good specimens of the material would perform satisfactorily with an ordinary cat's whisker contact.
Carborundum : Carborundum, or to give it its chemical name, silicon carbide, SiC, is a particularly hard substance that even today is used as a semiconductor. Even in the 1920s it was known to be able to withstand very high temperature's without any loss in performance, although why this would be of use was not stated.
Silicon carbide occurs naturally as the very rare mineral named moissanite. However, silicon carbide powder has been mass-produced since 1893 for use as an abrasive.
Constructors of crystal radios in the 1920s used these crystals and experimented with the different types to gain the optimum performance. Stockists of the various parts required for making wire-less sets would normally be able to provide a variety of different crystals and the assemblies in which they were mounted.
73 Scott KF5JRV
KF5JRV.#NWAR.AR.USA.NA
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