litude, created by the arrival of the gamma pulse. The output of
, volts
anetining Meceabrater was differentiated and applied to the grid of the head-switchingrelay network.
Head-Switohing Assembly: The assembly consisted of a monostable multivibrator
with a relay as plate load for the “on” plate, controlling Relay K-310, which controlled
the state of Relays K-411, K-412, K-413, and K-414.
The plate Relay K-309 was ener-
gized with the turn on of the syatem and remained energized until the arrival of a positive
pulse from the timing multivibrator. Relay K-309 received plus 12 volts through the
normally closed contacts of K-309 and, in turn, controlled the plus 12 voltage applied
through K-310 normally closed contacts to Relays K-411, K-412, K-413, and K-414.
Upon arrival of the positive pulse from the timing multivibrator, the head switching relay multivibrator changed state, de~energizing relay K-309, energizing K~310, and de-
energizing Relays K-411, K-412, K-413, and K~-414.
Relays K-411, K-412, and K-413 were the head-switching relays.
When they were
energized, the output of the {mpedance converter was applied to the record head; when
de-energized the recording heads were grounded. Relay K-414 controlled the tape speed,
and when energized, the magnetic clutch from the record motor was energized, connect{ng the record motor to the capstan. When Relay K-414 was de-energized, the clutch for
playback was activated, and the playback motor was comnected to the capstan. Relay
K-801 controlled the record drive motor and turned it off in the playback mode.
Relay K-414 alsc controlled the 350~ko drive to the erase amplifier. When K~414
was de-energized, K-414 grounded the ‘nput to the erase amplifier.
Relay K-310 obtained plus 12 volts of holding voltage from the encoder network, and
when it was applied the magnetic recording system went through one cycle, after the
arrival of the 10-,sec pulse from the adder channel. If this voltage was not present,
the system would not shift down into the playback mode.
2.3.3 Erase Electronics. Erase Amplifiers: The erase amplifier consisted of a drive
amplifier and two push-pull amplifier networks. The drive amplifier was a single-triode
amplifier with gain sufficient to provide 350 kc drive voltage to the power amplifiers.
The power amplifiers were operated Class AB,, and were capable of providing 10 watts
into a load impedance of 10,000 ohms. The erase head was composed of eight erase
tracks, each track having an impedance of 10,000 ohms, so when connected in series
paralleled with three other tracks, an impedance of 10,000 ohms was obtained. Each
push-pull network drove four erase tracks, each track having a power input of 2.5 watts.
Each network had two adjustable controllers, one to provide alternating current balance,
the other to provide the direct current balance. The direct current balance was critical,
because there would be direct current in the erase windings and a direct current unbalance of 4 ma would erage the tape after the drive signals had been removed. The alternating current balance was necessary to obtain low distortion in the 350-ke signal. If
distortion was present, it would create a direct current bias of the tape. The result of
direct current bias on the tape could be serious second harmonic distortion of the recorded signal.
Transport: The transport was driven by two “globe” permanent-magnet, governor-
controlled, motors. The governors were centrifugal and required arc suppressors to
prevent contact arcing from getting into the power line. The record motors turned at
2350 rmp and the playback motor at 152 rpm. Attached to each motor were magnetic
clutches gear-linked to a pulley that, in turn, drove the capstan at either the high or
low speed, depending on the position of relay K-414.
The record head was a Brush-Clevite magnetic head. This head contained eight
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