5262 HYDROGEAPHIC MANUAL PaGE 482 



by protecting the transceiver from spurious electric noises arising in the rectifier circuit. This filter 

 is housed in a watertight cast-metal box, size 10}i by 10^ by 8 inches, known as the filter junction box. 

 The transceiver is energized by 17.5-kc power generated by a vacuum-tube oscillator and amplified 

 to about 150 watts. A push-pull electron-coupled oscillator, employing type 59 tubes, generates the 

 oscillations. The 17.5-kc frequency of the oscillator is determined by an inductance-capacitance 

 combination, and can be varied through a range of a few kilocycles by means of a variable condenser. 

 The oscillator is followed by an intermediate amplifier composed of two type 807 tubes arranged in 

 push-pull. This stage is, in turn, coupled to the last power-amplifier stage formed of four type 838 

 tubes arranged in push-pull parallel. The plate circuits of these tubes are coupled to the transceiver 

 by means of a transformer whose secondary is tuned to 17.5 kilocycles by means of a series 0.012 micro- 

 farad condenser located in the filter junction box. Both amplifier stages are biased beyond cutoff 

 and may be considered as class-C amplifiers. The oscillator and power amplifier are located in the 

 top compartment of the power supply. 



5262. Echo Amplifier 



The echo amplifier is housed in a metal case, size 23}^ by 13)^ by 13 inches, so arranged that it is 

 accessible either by lifting a cover or by pulling out the entire subassembly in very much the same 

 way a drawer would be pulled out. The estimated total weight of the echo amplifier is 140 pounds. 

 The echo amplifier employs a superheterodyne circuit, designed so that the 17.5-kc echo voltage is 

 first amplified to some extent and then is increased in frequency to 175 kilocycles, at which frequency 

 it is amplified further. The input transformer which couples the transceiver to the first type 6K7 

 amplifier tube is tuned to 17.5 kilocycles. In the plate circuit of this tube is another transformer 

 tuned to the same frequency, which couples it to the type 6J7 detector tube. In the control grid 

 circuit of the type 6J7 detector, voltages of two frequencies are mixed — the 17.5-kc echo voltage is 

 mixed with that from a separate oscillator whose nominal frequency is either 157.5 or 192.5 kilocycles. 

 A 17.5-kc echo voltage when added to a 157.5, or subtracted from a 192.5-kc voltage, through the detec- 

 tor action of the type 6/7 tube will result in a 175-kc voltage. This 175-kc voltage is amplified by 

 the succeeding two type 6K7 tubes, in whose plate and grid circuits are coupling transformers tuned 

 to 175 kilocycles. The last tube of the amplifier is a detector, by whose action, in conjunction with a 

 low-pass filter, the 175-kc voltage is eliminated, leaving the rectified envelope of the echo signal. 



By means of a "shoal-deep" switch on the front panel of the amplifier the Q (figure of merit) of 

 the input transformer and of the second 17.5-kc transformer may be reduced, which is advantageous 

 in shoal-water sounding. When sounding in deep water it is often desirable to listen for the echo 

 through headphones or a loud speaker. Since the frequency employed in the amplffier is above the 

 audible range, it must be reduced in frequency to be heard. This is accomplished by means of a cir- 

 cuit, composed of an oscillator, detector, and associated circuits, which reduces the second harmonic of 

 175 kc, which is 350 kc, to an audible frequency. After additional amplification the echo signal 

 can be heard in headphones, or a loud speaker, plugged into a jack on the front of the amplifier panel 

 or into one on the face of the indicator cabinet. This echo-listening circuit can be turned ofT and on 

 by means of a toggle switch. When it is in operation a green pilot lamp, located on the face of the 

 amplifier, is lighted. The high-voltage rectifier and filter circuit is included in the amplifier cabinet 

 to furnish the necessary plate and filament power for the tubes. Besides those parts located on the 

 front of the amplifier panel that have already been described, there is an off -on switch for the amplifier 

 circuit, an amber pilot lamp to indicate the operation of the amplifier, and a 0- to 1-milliampere 

 d-c meter connected in the plate-circuit output of the type 6B8 tube. 



5263. Indicator 



The visually indicating mechanism is housed in a cast-metal cabinet, size 26 by Id^i by 13 inches, 

 whose total weight is 200 pounds. This cabinet has a hinged front that may be lowered to a horizontal 

 position, and a section of the top is also hinged to furnish access to the interior. The right-hand 

 section of the front is a rectangular hinged frame, about lili by 11 inches in size, in which is set a 

 glass plate which contains the depth scales. Directly above the frame is a glass window through 

 which to view the starting stroboscope. On the left side of the front panel are the following 

 numerous controls: a 5-point selector switch for starting and for selection between sonic and 

 supersonic signals; another 5-point selector switch which permits the use of any one of thg three 

 depth scales; two gain controls, one for the sonic and the other for the supersonic echo amplifiers; 

 two push buttons, one to operate the starting motor and the other for manual deletion of the trans- 



