The inputs were applied directly to the impedance converter, which provided the nec- essary amplification and frequency pre-emphasis. The output of the impedance converter was mixed with the output of the isolation amplifier before being applied to the recording head. The recorder was always in the record mode when the system was turned on, and the data that was recorded was played back and erased before new data was recorded. The input to Channel 1 was also applied to the input of a monostabie multivibrator. This multivibrator was used to provide a positive pulse, delayed by 120 msec from the arrival of the 10-usec pulse. The delayed positive pulse was applied to another multivibrator, which performed the function of shifting the recorder to the playback speed of 3° in/sec, turning the erase drive off, and removing the recording signal by grounding the recorder heads. The playback head was connected to the playback amplifier through a commutator, which provided signal switching, to enable the playback amplifier to play back each chan- nel of data twice. The commutator drive was connected to the recorder capstan drive to insure proper speed relationship in both record and playback modes. The playback amplifier provided the necessary gain to modulate the 70~kc voltage-controlled oscillator +18 percent. The frequency response of the playback amplifier was selected to provide the best operation from 50 cycles to 4 kc with a maximum signal-to-noise ratio being the prime consideration. The erase amplifiers were necessary to erase the signals recorded prior to the arrival of the desired signals. The erase was turned off after the desired signals had been recorded. The length of recording time waa 120 msecafter the arrival of the gamma pulse. 2.3.1 Recording Electronics. Impedance Converters: The unit contained seven impedance converters. This application required the use of six converters, the seventh being used as a sparein the event of a failure of one of the active impedance converters. The impedance-converter circult consisted of a dual triode connected in parallel to obtain a low plate resistance to provide maximum power delivery into the low-impedance record head. The stage was designed to provide a constant recording head current with a constant input voltage for frequencies between 500 cycles and 50 kc. The grid input network was designed to provide a 6 decibel/octave roll off from 100 cyclea to 7 kc, with 7 kc, being down 21 decibel, and rising 6 decibel/octave from 10 ke to 50 kc, with 50 ke down 7 decibel with respect to 100 cycles. The current-delivering capability of the impedance converter was 1 ma at 10 kc maximum. Isolation Amplifiers: The unit contained seven isolation amplifiers and, as with the impedance converters, only six were used, with the seventh as a spare. The isolation amplifiers provided biag current to the record head. The circuit consisted of a dual triode connected in parallef to obtain the current-delivering capabilities to deliver 10 ma, at 350 ke, into the record head. The voltage gain of the network was 2.3, with primary design consideration being current delivered into a low-impedance load. Bias Oscillator: The bias oscillator network was comprised of a twin T oscillator driving a cathode follower. The twin T oscillator circuit was selected for its simplicity and frequency stability over temperature and voltage changes. The cathode follower performed the function of a buffer and of matching impedances. The cathode follower drove all isolation amplifiers in parallel, representing a load of 10,000 ohms. 2.3.2 Timing Electronics. Timing Muldvibrator: This provided the proper length of recording cycle. The monostable multivibrator had a negative output pulse 85 volts peak amplitude and a duration of 115 msec. The multivibrator was triggered by a 10-,sec 25