CARRIER SYSTEMS ON TELEPHONE LINES 



615 



them from flowing through the plate battery. The carrier current in 

 the plate circuit divides between two paths, one through R-2, the feed- 

 back resistance to the grid circuit, and the other through R-3, the 

 output resistance, and the transformer T-2 which impresses the 

 carrier voltage on the grids of the modulating tubes. The filaments 

 of the tubes in the modulator circuit are wired in series, and the 

 current flow is regulated by a ballast resister B. 



Figures 33 and 34 show the front and rear views of the modulator 

 panel. The adjustable condensers which control the carrier frequency 



Figure 34 — Assembly of modulator panel. (Rear view) 



and the carrier balance are accessible from the front of the panel. 

 In the rear view, the oscillator circuit occupies the left-hand side of 

 the picture. The oscillating transformer is in the upper left-hand 

 corner, with the oscillating condensers directly below it. The feed- 

 back and output resistances are connected across the top of the panel. 

 The oscillating tube is left of the three tubes, and the carrier input 

 transformer is below it. The voice input transformer is to the right 

 of the carrier transformer, and the output transformer is located in 

 the upper right-hand corner. A metal cover fits over the complete 

 panel at the back to provide electrical shielding and mechanical 

 40 



