The spring for tensioning the rubber idler against the tape capstan 

 should be designed to place a firm pressure on the tape. If the tension 

 is insufficient, it will allow the tape to be pulled through the capstan 

 roller by the take-up reel, resulting in a tape speed too fast for proper 

 recording. 



If the tape recorder is turned off, the capstan roller must be 

 backed off from resting on the capstan. If the roller is allowed to 

 stand on the capstan with pressure, the rubber roller will indent perma- 

 nently and be rendered useless. Removal of pressure on the capstan is 

 accomplished by placing a pin through the roller bracket into a hole 

 drilled in the front panel. 



The recorder requires a timer for placing the internal calibration 

 signal on the tape automatically. Figure 47 shows assembly and wiring 

 of this timer. The timer cable plugs into the octal socket on top of the 

 tape-recorder chassis. Calibration of the tape recorder requires a 

 calibration unit which is fabricated according to Figure 48. Parts 

 required are listed in Table XI. 



3. Calibration and Operation 



The wave signal from the gage must have an amplitude that will 

 provide a current of 0.8 milliampere through the magnetic tape head. 

 The voltage level from the wave gage should be greater than 5 volts for 

 the tide capacitor in the tape recorder to have an adequate time constant. 

 The wave signal from the CERC wave gages is more than that required, and 

 the signal level is reduced and adjusted by the potentiometer in the lower 

 center adjusting-port in the front panel of the tape recorder. See 

 Figure 49. 



The bias frequency to the tape head must be 8.0 milliamperes, and 

 is adjusted by the potentiometer located through the port on the bottom 

 right from center panel position. 



The internal 4-second period calibration signal also must provide 

 0.8 milliampere through the magnetic tape head. This signal will be 

 indicated by the left meter on the tape recorder panel. The meter will 

 swing 400-0-400 microamperes when properly adjusted. A centering control 

 on the inside chassis of the recorder is provided to center the calibra- 

 tion signal on this meter. 



Calibrate the tape recorder by the following steps: 



a) Turn all controls recessed in the three ports in the bottom 

 center of the recorder panel to their counterclockwise 

 positions . 



b) Set the centering control on the recorder chassis to its mid- 

 point of rotation. 



Text resumes on page 98 

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