102 



BELL SYSTEM TECHNICAL JOURNAL 



System Maintenance 

 Arrangements are provided whereby the tubes may be tested on a 

 routine basis as has been done in voice-frequency practice. The 

 ampUfier panels, however, are provided with test jacks which are con- 



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Fig. 19 — Testing oscillator. 



nected to resistances in the plate circuits. A reading of the voltage 

 across the resistance gives a measure of the plate current for the 

 associated tube without disturbing the amplifier performance while 

 the amplifier is in service. A portable tube testing set. Fig. 18, has 

 been designed for this measurement. 



