Page 485 



ECHO SOUNDING 



5265 



On the lower panel are three meters; a 0- to 1,500- volt d-c meter to indicate the voltage of 

 the high-voltage rectifier circuit, a 0- to 150-volt a-c meter to indicate, the supply-line voltage, and 

 a 0- to 2-ampere d-c meter to indicate the polarizing current flowing through the^ transceiver. In 

 addition to these meters there are two toggle switches on this panel, one to operate the 110- volt line 

 relay, and the other to turn on the high-voltage rectifier. 



The tuning fork and its circuits furnish 1025-cycle power to the synchronous driving motor. 

 The tuning fork, made of low temperature coefficient steel, is of conventional design. It is driven 

 by a two-tube amplifier. Adjacent to the fork tines are two coils: one is a headphone receiver, known 

 as the pick-up coil, which is magnetically coupled to the outside of one tine; the other is an iron-core 

 coil, known as the driving coil, which is located between the fork tines. The input of the vacuum- 

 tube amplifier is connected to the pick-up coil, and the output is connected to the driving coil. The 

 tuning fork forms a coupling between the input and output of the amplifier, permitting oscillations 



Figure 108.— Power supply rack of Dorsey Fathometer No. 3. 



at a frequency determined by the tuning fork. Part of the voltage of this circuit is used to operate 

 a type 6i^6 tube amplifier, whose power output is further amplified by two type 838 power tubes 

 arranged in a push-pull circuit. 



On some ships of the Coast and Geodetic Survey the primary source of power to operate the 

 Dorsey Fathometer No. 3 is a 110-volt, 5-kva turbogenerator, but on other ships a d-c to a-c rotary 

 converter is used for this purpose. 



There have been cases where the 5-kva turbogenerator governor has failed to function. Such 

 failure may result in high voltage sufficient to damage parts of the Fathometer. On one ship, governor 

 failure was frequent enough to warrant the installation of an overvoltage circuit breaker. In any 

 case, the capacity of the fuses placed in the supply line should not exceed 30 amperes for a normal 

 Dorsey Fathometer No. 3 installation. 



