"Doping" Coils

Radio Record, Volume III, Issue 11, 27 September 1929, Page 30

"Doping" Coils

Renders them MoistureProof | the moist weather a coil which is "low-loss" on one day may be "high-loss" on the next, owing te the absorption of moisture by the cotton or silk covering of the wire. At one time it was thought that silk-covered wire was fairly immune to moisture effects, but careful tests show that silk absorbs moisture just as easily as the cotton covering. It is always wise to dry the coil thoroughly after winding and to "dope" it with some suitable material. Com paratively few substances: are better than celluloid dissolved in amyl-ace-tate. Obtain some amyl-acetate from the chemist and put it in a wide-mouth-ed bottle, securely corked. Remember that it is highly inflamable! Take any old scraps of celluloid and put them in the bottie with the amyl-ace-tate, and after a time they will dissolve. Old photographie films from which the gelatine covering has been removed by soaking in hot water and scraping is a very good source of supply. When the solution has become fairly thick, but not so thick that it will not spread easily, take a well-dried coil and brush on the "dope" fairly liberally. This "dope" serves the double purpose of waterproofing the wire and holding it in position on the former. A very useful tip when winding coils on paxolin, micanite or pirtoid tubes is to paint three thick strips of celluloid solution in the direction of the axis of the coil and about equally spaced before winding is begun. Now let the "dope" get "tacky." Proceed with the winding and each turn will adhere at three points. The whole coil can subsequently be "doped."