5267 HYDROGRAPHIC MANUAL PaGE 494 



((7) Indicator power supply.— Test the rectifier tubes (type 83 for positive, and type 82 for negative voltage). Test tlie various cir- 

 cuit elements. In case of failure of hydrophone current (24), test the elements of the resistance-capacitance filter in the indicator, 

 the inductance-capacitance filter in the sonic amplifier (53) and the milliammeter in the indicator. 



(ft) Selector switches.— Examine the physical condition of the specified half-sections of the wafers of the starting-frequency and 

 depth-selector switches (25-42). Test the continuity of the specified half-sections on the indicated switch positions. In 

 most cases either an a-c or a high-resistance d-c voltmeter, depending on the circumstances, may be used to determine the proper 

 functioning of the switches. Care must be used in measuring voltages on the starting-frequency switch, because the plate circuit (36) 

 of the type 807 keying tube (14) is 1,000 volts, or more, above ground. The highest voltage on the depth-selector switch is 300 volts. 



Spare wafers for these switches should be kept on hand. Inspection will show that three different types are used. 



(i) Starting motor.— The squirrel-cage motor winding of the starting motor is on the same shaft with the synchronous motor (47). 

 The starting motor (43) operates on the split-phase principle and is furnished with voltage from the combination of an autotransformer 

 (45) and a 4-microfarad condenser (4fi) . The stator is so connected through the starting-frequency switch (37i) that the motor furnishes 

 more torque on the second position of this switch than on the third position. The purpose of the reduced torque is to facilitate the 

 operation of synchronization. 



If the starting motor (43) fails to reach proper speed for synchronizing, it may be found that it will do so when the front lid of the 

 indicator cabinet is fully opened. 



(j) Synchronous motor.—The driving motor (47) in the indicator cabinet will sypchronize when brought to synchronous speed, if 

 furnished with ample 1025-cycle power. In some cases 85 ampere of 1025-cycle current flowing through this motor (as measured after 

 synchronization) is sufficient to ensure that the motor will not drop out of synchronization and stop, while in other cases as much as 

 l.l amperes is normally required. If the synchronous motor (47) fails to synchronize after the necessary warm-up period, or if it stops 

 after running a while, the reason may be that the torque required is too great, due to abnormal friction. Something may be touching a 

 moving part or the bearings may need lubrication. All bearings should be lubricated once each year. Turbine oil may be used for 

 this purpose. It should take at least 2 minutes for the synchronous motor to come to a stop after the power is turned off with it at 

 synchronous speed, and most instruments, on the average, require 3 minutes. 



■ (fc) Tuning-fork current.— If no current is flowing through the synchronous motor (47), no 2050-cycle tone from the indicator cabinet 

 will be heard. The trouble may be in the motor itself, in the circuit connecting it to the 1025-cycle power supply, or in the 1025- 

 cycle power supply itself. If the tuning fork (48) fails to vibrate, test the two type 6C5 tubes in the tuning-fork circuit (49) and measure 

 the voltage supplied to their plate and grid circuits, comparing the values with those given in table 18. Also test the various related 

 circuit elements The tuning-fork circuit (49) is rather critical with respect to grid voltage. The value given in table 18 is only an 

 average figure, and some circuits may require a different value. When the grid bias is properly adjusted, the tuning folk (48) will 

 always start vibrating and continue indefinitely, neglecting other considerations, and the grid-bias voltage should be adjusted with 

 this criterion solely in mind. The presence of magnetic or other foreign particles in the air gap between the fork tines and the electro- 

 magnets may prevent the vibration of the tuning fork. The tines of the fork (48) should be centered roughly with respect to the driv- 

 ing magnet. The angular orientation of the pick-up magnet has some influence on the starting of the tuning fork but should not be 

 moved more than about 10^ from the original angle, and should be readjusted only when other means fail to cause the fork consistently 

 to start vibrating when the voltage is applied. The pick-up magnet should not be adjusted in order to change the current through 

 the synchronous motor (47). 



If the fork is vibrating, but there is no 1025-cycle output voltage, test the type 6/''6 tube, measure voltages supplied to its plate and 

 screen, comparing the values with those given in table 18. Also measure the high voltage supplied to the plates of the two type 838 

 power-amplifier tubes, as well as the various circuit elements associated with all three tubes (50) . 



If the synchronous motor (47) fails to synchronize, or if it drops out of synchronism and stops due to insufficient 1025-cycle current, 

 test the tubes and voltages in the power-supply assembly (50). Then if necessary, the 1025-cycle current may be increased by increas- 

 ing the voltage supplied to the plates of the type 6C5 tubes (49) which drive the tuning fork (48). However, the current through the 

 synchronous motor must be kept at a minimum to avoid possible damage due to excessive heating in the indicator cabinet. 



(0 Echo amplifier.— Test the tubes and circuit elements of the specified echo amplifier. Test the voltages supplied to the tubes 

 and compare them with the values given in table 18. Test the insulation of the input and output circuits. 



The 17.5-kc echo amplifier (51) must be retuned periodically. This may be accomplished in several ways. One of the most direct 

 methods involves the use, for tuning purposes, of the type 59 tube 17.5-kc oscillator (55) in the 17.5-kc power supply, and the use of the 

 1-milliampere d-c meter on the face of the echo-ampljfler cabinet as a means of tuning indication. 



If the 17.5-kc echo amplifier (51) is nearly tuned, only a very small value of 17.5-kc signal voltage will be required, and in all proba- 

 bility, sufficient signal will be picked up by the echo amplifier when the type 838 and type 807 tubes (56) are removed from the 17.5-kc 

 power supply. As in tuning most high-gain amplifiers, care must be exercised to avoid overloading in any of the stages. The second 

 detector stage begins to overload below about 0.75-milliampere plate current, as registered by the 1-milliampere d-c meter. Hence the 

 value of the 17.5-kc input signal and the gain of the echo amplifier must both be kept adjusted so that the tuning may be done with this 

 meter reading between about 0.75 and 0.8 milliampere. Various means of adjusting the value of the signal picked up by the echo ampli- 

 fier will suggest themselvas, and the range of gain control of the amplifier may be temporarily increased, it necessary, by adding resist- 

 ance to the gain-control circuit in the indicator cabinet. Normal procedure is followed in tuning the amplifier, using the minimum 

 reading of the meter as an indication of tuning for any given tuning operation. The type 59 tube 17.5-kc oscillator (55) may be caused to 

 oscillate continually when the starting-frequency switch is on position 4, by turning off the switch provided inside the indicator cabinet 

 for controlling the 110-volt 60-cycle current supplied to parts within. But this should be done only after the type 838 tubes have been 

 removed from the 17.5-kc power supply. 



For tuning the echo-listening channel (52) of the 17.5-kc echo amplifier (51), an oscilloscope may conveniently be used as a tuning 

 indicator. For this purpose the oscilloscope may be connected in place of the head receivers. With the type 59 tube 17.5-kc oscillator 

 (55) still oscillating continuously and with the types 838 and 807 amplifier tubes (56) removed, the audio beat-frequency oscillator should 

 be adjusted to produce an audio frequency of about a thousand cycles. Normal practice is then followed in tuning the 350-kc inter- 

 mediate frequency transformer in the audio channel. 



(to) 17.6-kc transmitter .-Measure the 17.5-kc current flowing into the transceiver (61) by pressing the test button provided for the 

 purpose on the upper panel of the power supply. Test the type 59 tubes in the 17.5-kc oscillator (55). Measure all related voltages 

 in the oscillator and amplifier stages (56) and compare the values with those given in table 18. Test all associated circuit elements 

 jjicluding the insulation and continuity of the output transformer. 



The 17.5-kc output current is to some extent a function of the keying-circuit adjustment, which is described in (c). The lack of 

 high-voltage d-c (57) may be due to failure of transformers, rectifier tubes, or condensers in the rectifier circuit; or due to failure of the 



