the erase head is on the Iefi)„ Thus the wire is magnetically clean before 

 any signal is recorded on it, During playback, the erase circuit is 

 inoperative o 



85 i For simplicity s the magnetic tape recorder will hereafter be referred 

 to. as "Mirrophone,'' W"here any great difference exists between operation 

 of the "Microphone" and the "Caltron", direct reference will be made to 

 the individual unit. In any case, each installation will contain either 

 two "Caltrons," or two "Mirrophoneso" 



Operation 



86, On the front of the Mirrophone are its operating controls. Two volume 

 . controls are available, one for the signal labeled ■ (normally aet 

 at about "7") and one for the 3-kc labeled (normally set at 



maximum). On the Caltron the power control switch is on the signal volume 

 control^ on the Mirrophone it is on the 3-kc signal control. This switch 

 turns on the power to both the magnetic recorder amplifier and tape unit 

 motor* 



87 o The large indicator knob on the front panel labeled MS is connected 

 to a 2, 5 r„p„m,, clock by a slipping sleeve engagement which permits it to 

 be moved by hand without damage to the clock itself,, When recording is' 

 started on the Mirrophone, this indicator is set at zero, and is then used 

 as an indication of recording time available , The indicator makes one 

 revolution in two minutes and thirty seconds. Maximum recording time avail— 

 able on the magnetic tape rgjijor der ^is two minutes and ^twenty^two seconds., 

 After this time, the first part of the signal recorded will be erased, Since 

 switching will consume some time, it is necessary to consider two minutes 

 and fifteen seconds as maximum recording time, determined as approximately 

 3/4 of a complete revolution from any starting position of the time indicator 

 knob, 



88., The control switch labeled has three positions marked 



, and 'mlhen the is switched to , the unit is 



ready to record the signal and 3-kc time tone pulses applied to it. When 

 the is in the ' position, the magnetic tape recorder is neither 

 recording nor reproducing although the motor is operating. It is in- a stand- 

 by condition and the previously recorded signal is preserved on the tape until 

 the operator desires to play It back. In the " position the amplifier 

 output is switched from the recording head to the time tone amplifier, and the 

 recording on the tape is made available for the re-recording operation on the 

 high-speed sound level recorder, During playback the .. control must 

 be turned back to 1 or off position for this control, but not for the switch 

 which is part of it, 



89 o On the panel directly above the magnetic tape recorder panel a tuning- 

 eye tube visual indicator is located (FigSo 6 and 9), This eye affords a 



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