118 



BELL SYSTEM TECHNICAL JOURNAL 



2k 

 >l 



ILI H 





2 4 6 8 10 12 14 16 18 20 22 



lOOO-CYCLE INPUT (O LEVEL) IN DECIBELS ABOVE 1 MILLIWATT 



Fig. 8 — Channel load curve at 1000 cycles. 



Maintenance Features 



Since the type "K" system provides more circuits in a group than 

 ever before, it is essential that appropriately better maintenance 

 facilities be furnished. Wherever vacuum tubes are used, jacks have 

 been included to permit testing the condition of the tube by plugging 

 in a new type of test set. The testing of a working tube with this set 

 will not produce an appreciable reaction on performance of the circuits 

 involved. When it has been determined that a tube in the common 

 equipment is nearing the end of its useful life, a special transfer cord 

 circuit is used to remove the circuit involving the tube from service 

 and to substitute a spare circuit temporarily while the defective tube 

 is replaced. This transfer from a regular to a spare and vice versa 

 can be made without effect upon service. 



