55° Ths recorrsra are shipped with 0=75 db potentiometers installed,, 

 This means thai the db lines inscribed on the recording paper are 7 1/2 

 db apart, givli g a total of 75 db for the writing width of the paper „ A 

 0-50 db potent ometer is included in the spare parts for each station. 

 This should be used only when very weak signals are being receivedo 

 When the 0-50 b potentiometer is used the lines on the recording paper 

 represent step, of 5 db each, or a total of 50 db for the writing width 

 of the paper o Care should be taken when handling the potentiometer to see 

 that the contact train, located on the underside, is not damaged in any 

 way„ The slider arm contact moves across this train to vary the potentio- 

 meter resistance „ Each week both contact train surface and slider arm 

 surface should be cleaned with carbon tetrachloride to keep contact resis- 

 tance at a minimum 



56 „ Directly in front of the signal-input potentiometer is a grey box 

 with two phone jacks and a switch,, The left jack receptacle labeled ] 



is connected across the output of the channel in use, and is for 

 monitoring purposes. Only crystal headphones should be used here The 

 other jack receptacle labeled allows the output of a radio 



receiver to be fed to the recorder for recording radio time signals from 

 the Bureau of Standards standard frequency station WWV on the recorder 

 tapes when making a chronometer correction,, While this is being done, 

 the spring-loaded switch between the jacks must be held in the RADIO T] 

 positions This eliminates all signal except that from the radio receiver, 

 which may then be read against the break-circuit chronometer time ticks „ 



57 o Across the rear of the chassis behind the shield supporting the 115- 

 volt AC relay are the recorder-amplifier tubes, with the exception of two 

 which are located under the chassis „ 



Sensitivit.1 



58. On the top of the chassis between the DC Milliammeter and the AC power 

 plug is a screw-driver adjustment labeled i This controls the 



sensitivity of the writing pen, and normally is turned fully clockwise for 

 maximum sensitivity,, 



Checking for Erratic Behavior 



59 o The meter, a DC Milliammeter ( 1O-O-10) , is a signal-indicating device 

 in the writing circuit. If the mechanical operation of the recorder is 

 correct the meter will read about when a steady signal is applied^ With 

 the motor turned off and the intensity of the input signal varied, the meter 

 should deflect to both sides of the center position approximately equally,, 

 This indicates that the amplifier circuit of the recorder is functioning 

 normally „ 



15- 



