PLATED QUARTZ CRYSTAL UNITS 247 



until it falls into its original position over the crystal plate. The solder is 

 then, fused to the wire and plate by means of a special aluminum tipped 

 soldering iron as shown in the illustration or by a controlled hot air blast 

 focused on the joint to melt the solder. In this operation a fillet or conical 

 button is formed around the wire attaching it to the silver spot. To pro- 

 mote good wetting of the solder, the spot should be clean and well burnished. 

 Rubbing the spot on a hard polished metal surface or burnishing with a 

 blunt pointed tool of agate, are the best methods found so far. 



The hot air blast has now replaced the iron entirely in commercial use. 

 It consists of a tube through which air at about one inch water pressure is 

 passed over a hot filament and through a nozzle directed at the solder. 

 The head of the filament is adjusted so that the temperature of the blast is 

 just hot enough to melt the solder and complete the attachment in 10 to 

 15 seconds time. In using this method with large plates care must be taken 

 to insure that the temperature of the crystal has reached that of the hot 

 plate and that the blast is brought up to the plate slowly, for otherwise the 

 heat shock of the localized blast may cause the crystal to crack. Fcr very 

 small plates the use of a hot plate may be dispensed with if the hot blast is 

 brought up slowly enough to preheat the crystal plate. Other means of 

 melting the solder such as a hot radiant wire or ribbon or the use of a minute 

 flame have been considered, but so far no extensive trials of these methods 

 have been made. The advantage of the hot blast over the other methods 

 mentioned is that it can be better controlled since little is left to the judg- 

 ment of the operator. If an iron is used it must actually be touched to the 

 solder with the possibility of displacing the position of the wire. Moreover, 

 as already mentioned, the iron must be equipped with a special aluminum 

 tip to prevent removal of solder from the joint on withdrawal of the iron. 

 Considerable maintenance is required to keep such irons in satisfactory 

 operating condition. 



13.45 Type of Wire Attachments 



The type of attachment described above wherein the part of the wire 

 embedded in the solder cone is straight was used in the first designs of wire- 

 supported crystals. However, it was found that with such attachments 

 vibration of the crystal plate caused breakage of the bond between the 

 solder cone and the wire with resultant failure of the attachments, especially 

 in large plates. Because of this the use of straight wires is recommended 

 only for small size plates. In order to eliminate the above difficulty a little 

 hook has been placed at the end of the wire embedded in the solder in order 

 to obtain a better anchorage. The hook is formed in the wire by means of 

 a special tool affixed to the soldering machine. The basic methods described 

 for straight wires are otherwise used for this type of attachment. Instead 



