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BELL SYSTEM TECHNICAL JOURNAL 



to the crystal and the coupHng between the crystal and wire vibrating sys- 

 tems. Considerable work has been done in regard to the amount of solder 

 necessary and the most desirable shape for the solder cone. The complete 

 assembly of a wire support for a crystal is shown in Fig. 8.4. The shape of 

 the solder cone shown in Fig. 8.4 has proved to be the most desirable and has 

 been termed as "bell-shaped." This type of cone formation allows the wire 

 to be twisted in handling and still not break away the top of the cone and 

 form an appreciable crater. For the purposes of analysis we may then as- 

 sume that the cone becomes part of the crystal and moves with it so that 

 when computing the length of a wire vibrating in flexure, this length should 

 be determined from the top of the cone. The amount of solder used in the 

 cone since it is part of the crystal must be kept at a minimum in order that 

 the constants of the crystal equivalent circuit will not be modiiied too much 

 by it. One established fact of the effect of the solder in the cone on the 



Fig. 8.4 — Soldered lead type movinting. 



equivalent circuit is to raise the resistance in the equivalent circuit for the 

 crystal and this resistance increases considerably with an increase in tem- 

 perature. The amount of solder permissible in the cone would then be 

 determined by the maximum temperature at which the crystal is to be oper- 

 ated and the minimum Q allowable. The type of motion that the crystal 

 would generate in the support wire when oscillating is that shown in Fig. 

 8.4 by the dotted line. The solder ball shown to the right of the figure acts 

 as the clamp for the wire. This solder ball may be placed at any point along 

 the wire corresponding to a node. The diameter of this ball need only be 

 sufficient to act as a clamp. In general, this will be in proportion to the wire 

 diameter. For example, at 200 kc it was necessary to use a solder ball 60 

 mils in diameter on a 6.0-mil diameter phosphor bronze wire. The spacing 

 between the solder ball and the head of the cone may be readily computed 

 from equation (8.1). In practice, it has been found that in most all cases 

 this distance is slightly greater than that given by the formula due to the I 



