CRYSTAL JOTTINGS

Radio Record, Volume I, Issue 21, 9 December 1927, Page 13

CRYSTAL JOTTINGS

The microphone bar amplifier is not used as much as it might be, but in many cases it will give good amplification and beter tone than a low-priced /two-valve amplifier when added to a crystal, The first cost of the bar. amplifier is low compared with a twovalve amplifier, and the running cost is very much less, In crystal rectification the current passes from the cat’s-whisker to the crystal. The principle of rectification allows very little current t pass_ in the opposite direction. It is alwavs worth while to try reversing your crystal connections so that current flows in the opposite direction, as it is frequently found that results are better with the current passing through the circuit in one direction than in the other. , Zincite crystals are both natural and artificial. For some time they have been manufactured as ‘‘synthetic" zincite, and give results equal to the natural variety. The synthetic crystals are hard, and not brittle, and may be used as oscillating or amplifying crystals. They are made bv heating in a furnace ordinary ‘zine white,"

such as is used in paint, with or without a trace of manganese dioxide. A cherry-red heat produces a_ yellowlooking, glassy mass, and when this is carefully broken and tested much of it will be found to be very sensitive to radio signals. Carborundum is carbide of silicon, and is manufactured by fusing a mixture of fine sand and coke in an electric furnace, This crystal is not attacked by acids of any kind. If purchased unmounted, the light steel-blue variety is best for wireless reception. Where selectivity is required in a crystal set, loose-coupled tuning should be adopted, as a slight variation in the coupling will often cut ont interference, and bring in the broadcast just the same. In Britain, where two stations are frequently simultaneously broadcasting the same programme on _ different wave-lengths, crystal sets are often used constructed with two separatelytuned circuits, one receiving each station, and these two series of signals, passing through the same ’phone, result in much increased volume. The volume is not usually doubled, because, as a rule, one station will be { situated at a greater distance than the other. A POCKET CRYSTAL SET. Next week there will be a special article describing the making of a handy pocket crystal set, ecsily made, cost very small, yet quite good for] permanent use near a broadcast cen- |: tre. Cyclists out for the day will be able to try this ont at various distances. A length of thin wire hitched to a tree makes a good temporary acrial, and the end of a wire run into a creek makes a good earth, whilst *phones occupy little space with the headbands temporarily removed. f