142 BELL SYSTEM TECHNICAL JOURNAL 



not have a continuous control of the plate current. When a positive poten- 

 tial is applied to the plate, current does not flow until the magnitude of the 

 negative grid voltage is reduced to the critical value, at which time the plate 

 current flows, and the magnitude of the plate current depends upon the 

 voltages and impedances in the circuit. The grid has no further control, 

 and plate current flows until it is stopped by reducing the plate voltage 

 to zero. 



Thyratron tubes use various gases and mixtures of gases. The earliest 

 type used mercury vapor, but this type of tube is quite sensitive to tempera- 

 ture changes. The grid characteristics are shifted materially by changes 

 in the room temperature in which it is operated, and in low temperatures 

 it is almost a vacuum tube. Thyratron tubes using argon gas are not 

 affected by temperature changes, but high-pressure argon tubes have a low 

 inverse voltage which limits their application to low-voltage rectifiers. 

 Tubes using low-pressure argon have a higher inverse voltage, but are ac- 

 companied by a high arc drop which makes their efficiency low. A mixture 

 of mercury vapor and argon has been found which provides the temperature- 

 stable grid characteristic of the argon tube and the low arc drop of the mer- 

 cury-vapor tube. This type of tube has been very successful with certain 

 regulating circuits, particularly at voltages less than 60 volts. 



Five kinds of regulating circuits are used in telephone offices to hold the 

 output voltage of rectifiers constartt. The selection of the circuit to be used 

 depends upon the magnitude of the current, d-c voltage, and type of recti- 

 fying means to be used. Two forms of regulating circuits using thyratron 

 tubes and one using two-element high-pressure tubes were developed. A 

 fourth circuit using all vacuum tubes was adapted for telephone use. The 

 fifth kind uses a negative resistance. 



In this paper a table shows the voltage and current output, type of control 

 of the rectifiers, and the rectifying means that have found widespread use 

 in the Bell System. 



The regulated rectifier finds its applications in telephone offices where 

 constant voltage, independent of load and a-c line-voltage variations, is 

 required to supply filament grid bias and plate voltage to telephone re- 

 peaters. Certain measuring circuits require a regulated rectifier to supply 

 a stabilized voltage. Regulated rectifiers also find applications where con- 

 stant voltage is of secondary importance but an automatic power plant is 

 desired for maintaining storage batteries in a fully charged condition to be 

 ready to supply the power for telephone offices if the a-c power fails. A 

 further compensation of regulating the voltage is the increase in life ob- 

 tained from storage batteries if they are not continually being charged and 

 discharged but are fully floated. 



