| [3] | The different detectors in order of their sensitiveness are electrolytic, perikon, magnetic, silicon, carborundum. |
| [4] | Peacock ore or bornite, which consists of about 60 parts of copper, 14 parts of iron and 26 parts of sulphur, may be substituted for the chalcopyrites with excellent results. |
CHAPTER XIV. TUNING COILS AND TRANSFORMERS.
A tuning coil is merely a variable inductance wound in single layer on a suitable form.
Fig. 121 illustrates a double slide tuner. The base is a piece of hard wood, 12 inches long, 1 inch thick and 5 1/2 inches wide. Two wooden heads 4 x 4 x 3/4 inches support the form upon which the coil is wound.
Fig. 121. Double-slide Tuning Coil.
The form is a piece of wooden curtain pole, 9 inches long and 3 inches in diameter. Some may prefer to use a cardboard tube in place of the curtain pole. A tube can be made by winding a long strip of cardboard 9 inches wide around a suitable form and cementing the layers together with shellac. The liberal use of shellac will stiffen the tube and cause it to better retain its shape. The tube is held tightly between the two heads by means of a brass rod which passes through the center and is clamped by two nuts.
A square brass rod 10 1/2 inches long is fastened to the center of the top of the heads and a similar rod to the center of the front face.
