576 BELL SYSTEM TECHNICAL JOURNAL 



The crystal itself is no problem as far as continuity of operation is con- 

 cerned. Its motion is so very small there is no likelihood at all of failure on 

 that account. Mountings are very stable and in all likelihood will be 

 improved. The oscillator circuit, the frequency demultiplier, the power 

 amplifier and the temperature-control circuit are all vacuum-tube devices 

 and deserve special consideration. In all of these circuits, vacuum tubes 

 have been used in some installations which do not have a very long life, 

 some even becoming defective within a year of operation. On the other 

 hand, there are tubes which have been developed for use in continuous 

 telephone circuits where failures would be troublesome and costly. Some of 

 these tubes in current production have an expected life of more than ten 

 years. There is good reason to believe that a quartz clock installation 

 equipped with such vacuum tubes throughout, and engineered so as to make 

 effective use of their special properties, would operate continuously for ten 

 years or more. 



The remaining 'link" in the chain is the synchronous mechanism operated 

 from the crystal-controlled circuits and used for totalizing continuously the 

 oscillations of the crystal and for producing suitable time signals at specified 

 intervals of time thus measured off in terms of the crystal rate. This 

 mechanism usually consists of a small synchronous (phonic wheel) motor 

 operated from a submultiple of the crystal frequency and geared to com- 

 mutators or cams or other means for producing the electrical signals used 

 in making time measurements. Many of the troubles in quartz clock in- 

 stallations have occurred in this 'link'. There is every reason to believe, 

 however, that suitable synchronous motors geared to cam-controlled elec- 

 trical contacts can be built that will operate continuously through many 

 years. To insure long operation it would be desirable to employ motors 

 with low rotation speed in order to reduce bearing wear. With the present 

 knowledge of bearing materials and lubricants, it should be a simple matter 

 to design such a motor that would operate without failure for ten years or 

 more. 



A relatively trouble-free electrical time signal producer, suitable for 

 operating under the control of a quartz oscillator, with frequency demulti- 

 pliers to 100 cycles, could be constructed as indicated schematically in Fig. 

 34. This is not intended to be an actual design, but is intended to indicate 

 how an apparatus could be designed that would circumvent some of the 

 troubles now experienced which prevent long continuous operation. 



The basic apparatus consists of a crystal oscillator, presumably 100,000 

 cycles, with a frequency divider to obtain controlled 100-cycle current to 

 drive the 100-pole phonic wheel motor at one revolution per second. Ob- 

 viously, other crystal frequencies and step-down ratios could be used, the 



