Page 493 



ECHO SOUNDING 



5267 



Table 18. — Circuit voltages of Dorsey Fathometer No. S — Continued 

 [This table assumes 60-cycle line supply of 110 volts which is the value at which the instrument should normally be operated.] 



Terminal 



post 

 number 



Voltage or current 



Power Supply — Continued 

 D-C Sup-ply: 



Polarizing current to transceiver 



High voltage 



11-12 

 39 



Amplifier 

 17.5-Kc Echo Amplifier: 



Plate circuits 



Screen circuits . 



Plate current of type 6B8 (measured by meter in face of 

 cabinet) . 



1.7-1.8 amperes. 

 1,350 volts. 



250 volts. 

 110 volts. 

 0.8-0.85 ma. 



In the following paragraphs lettered (a) to (r), the reference numbers refer to elements and parts 

 as numbered in table 14: 



(a) Photoelectric tube testing and adjusting.— Measure the voltage at the anode of the specified photoelectric tube (1, 2, 3, 4, or 6) 

 with a high-resistance d-c voltmeter and compare with the value given in table 18. Type 921 photoelectric tubes are gas-filled and will 

 not function properly in this Instrument at 90 or more volts. Measure the continuity from the grid of the type 6^5 keying tube (11) 

 to the cathode of the specified photoelectric tube. 



Ensure that the socket makes good electric contact at both ends of the specified photoelectric tube by cleaning the contact areas 

 of both ends of the tube and the socket. 



Determine if the specified photoelectric tube is held tightly in its socket and, if not, remove the tube and bend the socket ends 

 slightly in such a manner as to hold the tube firmly. The slotted light-shield must first be removed before removing either photo- 

 electric tube 1 or 2 in order to avoid excessive bending of the socket ends when removing or replacing the tube. These tubes are 

 supported at the ends of the two arms and are energized by light reflected from the concave mirrors. 



In case photoelectric tube 1 or 2 is specified, determine if the spot of reflected light passes near the center of the slot in the light- 

 shield and, if not, adjust the corresponding mirror by gently bending the mirror frame a slight amount, using care not to break the 

 mirror. In case photoelectric tube 3, 4, or 5, each of which receives light directly from its associated exciting lamp, is specified, be 

 sure that the photoelectric tube is nearly centered with respect to the beam of light and hence is completely illuminated by the 

 uninterrupted beam (see 5542) . 



Replace the specified photoelectric tube, if necessary. 



(6) Exciter tamps.— If exciter lamp 6 or 7, supported on the ends of the arms adjacent to photoelectric tubes 1 and 2 respectively, 

 is to be replaced, regular Mazda type 1130, spherical clear bulb, 6-8 volts, 21 ep, double-contact, bayonet-base lamps should be used. 

 When any of the other three exciter lamps (8, 9, and 10) is to be replaced, a special lamp must be used which has a tubular 5i-inch 

 clear bulb ( T-5) , but with base and filament similar to the above type. The latter special lamps with T-5 bulb may be obtained from 

 the Washington Office, and several should be kept on hand. 



After any lamp is replaced it is usually necessary to readjust the corresponding index (see 5542). 



(c) Keying circuit adjustment— supersonic system.— Test the specified tubes (11, 12, 13, or 14). Measure all related voltages and 

 compare with corresponding values in table 18. Test all circuit elements. 



When the supersonic system is being used, if there is evidence that the keying circuit is not operating properly and is in need of 

 adjustment, proceed as follows: Set the depth-selector switch on position 1 and the starting-frequency switch on position 4. In the 

 top compartment of the power supply is a potential divider with four adjustable taps. Measure the voltage to ground of the two 

 taps nearest to ground potential on this divider. If the voltages measured at these taps are not 200 and 500 they should be adjusted to 

 be so. If the circuit then fails to key the vacuum-tube oscillator (55) properly on the first four positions of the depth-selector switch, 

 the 500-volt tap should be moved slightly closer to ground. On the other hand if the oscillator (55) appears to key too readily as evi« 

 denced by continuous oscillations through a whole cycle, or a portion of a cycle greater than the normal signal, when the depth selector 

 is on position 3 or 4, for example, then the 500-volt tap should be moved to a slightly higher value. The third and fourth taps above 

 ground should then be adjusted to 200 and 500 volts above the final value of the second tap, as measured with the depth-selector switch 

 on position 1. 



(d) Keying circuit adjustment — sonic system. — If the keying circuit does not operate properly when the sonic system is being used, 

 the keying circuit voltages should be adjusted as described in (c). If the sonic keying relay (60) stUl fails to function properly, the 

 voltage at the plate of the type 807 tube (14) in the indicator should be measured and adjusted to some value between 1,100 and 1,300 

 volts. If the relay (60) fails to function when the voltage is 1,300 volts, the relay contacts must be inspected and cleaned if necessary. 

 In any case, the contacts should be adjusted to as small a separation as possible without risk of faUm-e to interrupt the current flowing 

 into the type 324 oscillators (63). And furthermore, the voltage supplied to the plate of the type 807 keying tube (14) should be kept 

 as low as possible. 



(e) Index neon tubes.— 'Exa.mine the physical condition of the specified index neon tube (15, 16, or 17). Check the ground connec- 

 tion on one end of the specified neon tube. Measure the polarizing voltage (21) supplied to the other end of the specified index neon 

 tube. 



(J) Index gas discharge tubes.— Test the specified type 885 tube (18, 19, or 20). Measure the values of voltage (22 and 23) supplied 

 to the specified type 885 tube and compare with the corresponding values in table 18. Test the circuit elements associated with the 

 specified type 885 tube, including the insulation and continuity of the transformer in the plate circuit. 



