TRANSATLANTIC CABLE POWER SYSTEM 151 



this meter is not arranged for calibration. However, the series resistors 

 incorporate 6,000-volt components for an extra degree of rehability. The 

 voltmeter with its series resistor is normally connected across the com- 

 mon cable power supply ahead of the cable current regulating point. It 

 can, however, be switched to read the cable voltage nearer the cable 

 termination. In the latter position, it reduces the cable current by about 

 1 milliampere, causing an unbalance in cable regulation, and therefore 

 is not normally left in this position. The cable supply voltage is also 

 indicated by a recording voltmeter. 



Other meters are provided to indicate series tube plate voltages, dc 

 rectifier voltages, ac input voltages, series tube currents, test currents 

 for adjusting mag-amp operating limits, and the difference in current 

 between the positive and negative power supplies to ground. Since 

 many of these instruments operate at high potential, a special design 

 was used with the operating mechanism and scale depressed in the in- 

 strument case approximately 1 inch. This both eliminated possible 

 electrostatic effects on the instrument pointers and served as a safety 

 measure. 



DC REGULATION 



DC Amplifier 



The direct-coupled two-stage amplifier shown in Fig. 5 is characterized 

 by potentiometer coupling and cold-cathode gas-tube voltage stabilizers. 

 The biases are selected high enough so that linear operation is assured 

 even for a short circuit at the cable terminal. As is apt to be the case in 

 a direct-coupled amplifier, cathode temperature in the low -level stage 

 is critical. In this amplifier, a 5 per cent change in heater voltage results 

 in a 0.5 milliampere change in the cable current. 



The required precision of current regulation in these power supplies 

 can be expressed as representing a source impedance of not less than 

 100,000 ohms. To meet this requirement, the gain of the dc amplifier 

 was made as large as practicable with the plate and screen potentials 

 available from gas-tube regulators. Interstage network impedances are 

 high to reduce the shunt losses, and are proportioned to provide the 

 large biases mentioned above. Gain adjustment is provided by a variable 

 resistance in series with the cathode of the first stage. 



Shaping of the loop gain and phase characteristics to obtain margins 

 for stable operation is accomplished by means of the RC shunt (R9C1) 

 across the plate resistor for the first stage. The amplifier gain and phase 

 characteristics without this compensation are shown in Fig. 6. These 



