The Crystal Corner

Radio Record, Volume II, Issue 39, 12 April 1929, Page 31

The Crystal Corner

Full Wave Circuit HAVE constructed your "full-wave" erystal set described in the "Radio Record" of December 14, 1928, and I must say that I am more than pleased with the results. The circuit was adhered to with two exceptions, as fol- * low:-In place of the two fixed detectors I employed two complete carborundum units with potentiometers and small dry cells.~ The earth and aerial terminals were placed on a strip at the back. Ebony was used for the front panel-an excellent material and very easy to drill out and shape. ‘y Three miles from 2YA, using an S0ft. agrial and an earth consisting of three iain. water pipes driven down about sft. 6in. into rock and clay, reception on the speaker is of sufficient volume to be comfortably heard in a large room, particularly during night transmission. Connected to a two-stage amplifier and a speaker attached to a good gramophone, the tone and volume are amazing, and the condensers have to be turned down (almost closed) for restful reception. In fact, the volume is so great that I frequently disconnect my earth wire altogether, open the condensors about ten degrees and turn my detectors up about one quarter of their tr.vel. The volume is still good and of remarkable purity. Some weeks ago I transported the set complete with amplifier to a place about twenty miles away from 2YA, Connected ‘up to a good aerial and earth, "used a large cone speaker (which belongs to a five-valve set) and received the station at as great or greater volume than at the shorter distance. A very satisfying performance, Housed in a_ polished blackwood cabinet, which I constructed for it, the set has all the appearance of a threevalve outfit and is a source of endless pleasure to ali who hear it, The two detectors appear to be evenly matched, as volume is increased by both dials being turned to "ead the same. Variations in .vlume can also be obtained by turning the dials in opposition to one another, that is, opening one and closing the other condenser. The purity of tone remains the same until the variation is more than half the range, when a sligh’ blurring is noticed. Again expressing my appreciation of an excellent circuit-William J. McFjeon (Wellington South). Another Success. IN the issue of the "Radio Record" of December 14, 1928, you gave particulars of construction of a twoerystal set. I have carefully followed the directions and the completed set gives quite 75 per cent. increase in volume. In my set two catswhiskers are used in préference to semi-permanent or permanent detectors. My experience has beén that the former gives best results fc the distance we are from 2YA, viz.. 15 miles. Two dry cells are coupled to a bar amplifier. TY} results over my old single crystal set, which also used the bar amplifier, is as : tated above. A low range of hills intervenes between us and 2YA. Length of aerial 100ft., height 35ft. The earth wire is divided into four branches. This feature, also a suggestion fror’ the "Radio Record," has improved reception considerably. -A. P. Godber (Silverstream).