TRANSATLANTIC RADIO TELEPHONY 



121 



modulated carrier current which may get through the second modu- 

 lator circuit if it is imperfectly balanced. 



Having prepared at low power the side-band currents of desired 

 frequency it is necessary to amplify them to the required magnitude 

 for application to the transmitting antenna. This amplification is 

 carried out in three stages. The first stage increases the power to 

 about 750 watts, and is shown in Fig. 1 together with the modulating 

 circuits. This amplifier employs in its last stage three glass vacuum 

 tubes rated at 250 watts each and operating at 1500 volts. 



The output of the 750 watt amplifier is applied to the input of 

 the larger-power amplifying system beginning with the 15-kw. ampli- 



Fig. 2 



fier of Fig. 1. This consists of two water-cooled tubes in parallel, 

 operating at approximately 10,000 volts. The output of this amplifier 

 is applied by means of a transformer to the input of the 150-kw. 

 amplifier which consists of two units of ten water-cooled tubes each, 

 all operating in parallel at about 10,000 volts. 



The high-voltage, d-c. supply is furnished by a large vacuum tube 

 rectifier unit rated at 200 kw. It employs water-cooled tubes similar 



