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BELL SYSTEM TECHNICAL JOURNAL 



the condenser meshes with any stator or with parts of two adjacent 

 stators. The condenser, therefore, serves as a potential divider across 

 the regulating network sections, the loss introduced depending upon 

 the position of the rotor with respect to the stators. Basically these 

 artificial line sections consist of units having the same loss character- 

 istic. The first section, however, may be supplemented by additional 

 units which will be required on the shorter line sections in order to 

 build out the line slope as shown on Fig. 11. Since this section will 

 be the last one to be cut out by the regulator, the less accurate part 

 of the regulating range is thereby reserved for the periods of very 

 high line loss, such as during ice or frost formation which occurs only 

 infrequently. 



The second sensitrol relay has contacts which close only on much 

 larger changes in the pilot level such as would result from a failure of 

 the line itself. When it operates it disables the regulating circuit and 

 through a slow operating mercury relay brings in an audible or visual 

 alarm indicating to the attendant that the system is in trouble. 

 The slow operating relay introduces a delay in the operation so that 

 short interruptions will not operate the alarm system. 



The principal function of the regulating amplifier shown on Fig. 12 

 is to provide a high-impedance termination for the regulating network 

 and condenser combination. There is, however, a small amount of 

 gain available which may be useful in some cases. 



New Line Anplifier 



The amplifier which is used in the repeaters and in the transmitting 

 and receiving branches of each terminal is one of the outstanding 

 developments of the system. It was designed to have satisfactory 

 transmission characteristics over both upper and lower frequency 

 groups. It employs the principle of negative feedback ^ to achieve 

 a high degree of stability, freedom from modulation and stabilized 

 input and output impedances. 



The advances made in the design of this amplifier can be seen by 

 the comparison in the following table with the push-pull amplifier 

 which was used in the older systems. In some cases the latter was 

 supplemented by an auxiliary amplifier where higher gains were 

 needed. 



Push-Pull Amplifier 



Push-PuU Amplifier Plus Auxiliary 



Amplifier 



New Feedback Amplifier 



24-Volt 

 Power — - 



Watts 



52.8 



76.1 

 16.4 



130-Volt 

 Power — 



Watts 



15.1 



17.2 

 6.3 



Panel 

 Space — 

 Inches 



12i 



171 

 3i 



Gain 

 db 



32 



50 



No. of 

 Tubes 



