THE "RECORD" CRYSTAL SET

Radio Record, Volume I, Issue 6, 26 August 1927, Page 14

THE "RECORD" CRYSTAL SET

SOME ADDITIONAL NOTES-ALTERNATIVE TUNING

_; Several correspondents residing withfn a mile of 2YA are desirous of re@eiving that station at loudspeaker volume, using a crystal without amplifier. In our last issue the "Record" erystal set described is a good one with which td make the attempt. It can he done, but of course the error should mot be made of expecting boisterous yolume such as is given by a valve Set. The writer has heard several sessions through at a distance of twa miles, and the speaker volume was such that not a word of a lecture on Hollywood was missed, sitting three or four yards from the speaker, and. on Sunday, the 6th instant, the band concert music could be heard fairly well in an adjoining room. ‘This way of listening is more comfortable than wearing headphones, but quietness is necessary during reception. A carborundum erystal without battery was also tested and gave splendid results. For ’phone reception round the city and suburbs the neriali need not be of very great dignensions, ‘but of course the larger it is the more volume there will be. The earth connection is of very great importance in every case, and if this is made to a water-pipe (the cold water supply), care must be taken that the connection is a clean and tight metallic contact between the wire or earth clip and the pipe, which must be weil cleaned at the point of contact. In damp weather a water-pipe is ustially @ vety efficient earth connection, but in. dty weather it may in some cases’ prove otherwise. Dry sand is a bad conductor and in sandy districts, if signals are noticeably weaker after a

spell of dry weather, it is wise to replace the water-pipe earth with something more reliable. ‘This consists of some kind of metal plate sunk in the ground near the aerial to a depth of several feet, where the ground is always moist and damp. A copper plate about two feet square is the ideal earth plate, but a petrol tin with a 14’s wire soldered to it as an earth lead will serve quite well. An end of the tin should be cut out and earth, coke, or cinders put in. With one of such plates sunk near each aerial pole and counected by a buried wire, the same wire continuing to the earth terminal of set, best results are assured so far as the earth portion of the circuit is concerned. The coupling of the condenser in the ‘Record"’ set is that known as ‘‘parallel,’ but listeners can try the "series’’ coupling in an easy way as follows :- Disconnect the E terminal connection from the condenser, and in its place, on the condenser, connect the aerial direct, leaving the A terminal unconnected. The condenser will now give a much higher reading to tune in, and whether the result is better than parallel tuning can soon be judged. ‘The series tuning is an equivalent to reducing the number of turns on the coil for the lower broadcast wave-lengths. If it is desired to keep the set pevtnanently in series, then the present connections to A terminal should all be taken off, but still keeping condenser, crystal,~ and. coil connected. ‘The A terminal is then connected to the condenser terminal that was previously connected to #. The aerial is then connected to the A terminal as before.