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BELL SYSTEM TECHNICAL JOURNAL 



by by-pass condenser C-2, as they are at different potentials from 

 ground, due to the series connection of the filaments of the vacuum 

 tubes. The variable condenser C-3 affords a means of balancing 

 the carrier frequency potentials. Condenser C-4 is one half the 

 maximum capacity of C-3 in order that carrier frequency unbalance 



Figure 2>2i — Assembly of modulator panel. (Front view) 



in either side of the circuit may be compensated for to a sufficient 

 degree by means of the one adjustable condenser C-3. The voltages, 

 El and E^, provide the grid bias for the modulating tubes V-1 and 

 V-2. The condensers C-5 and C-6 provide a low impedance path 

 around the source of biasing potentials for the carrier frequency, and 

 condenser C-7 in the plate circuit performs the same function with 

 respect to the plate battery. 



In the oscillator, the condensers C-8 and C-9 together with the 

 inductance of one winding of the transformer T-4 form the oscillating 

 circuit. C-9 is made adjustable to compensate for manufacturing 

 variations in the inductance, and to provide in addition a certain 

 flexibility in frequency adjustment. A grid bias for the oscillating 

 tube is provided by the grid leak-condenser combination C. The 

 plate battery is connected through the retardation coil L-1, which 

 presents a high impedance to the carrier frequencies, and prevents 



