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Wind position
The working ts the same as in the REW position.
TS14 ts conductive. The mains voltage to the right
reel disc motor M2 is supplied via D9. The left motor
M1 works as a generator and supplies the mains
voltage for the circuit of the tape tension control!
via D12.
Tape tension control
The tape tension control works
in the position REW
or WIND. When the tape runs, one motor pulls and the
other is driven by the tape. To ensure constant drive,
the braking torque of the driven motor should vary.
The extent of the breaking torque the motor driven
should supply, depends on the diameter of the
reel (Braking torque = radius of the reel on the
motor pulled x force on the tape).
Maximum diameter of the ree! means maximum
braking torque of the motor driven.
Minimum diameter of the ree! means minimum
braking torque of the motor driven.
Maximum diameter of the ree! on the motor driven
The reel to be wound has the minimum diameter.
The pulling motor runs at maximum speed.
The voltage flowing through motor and R59 is
minimal. The voltage on the emitter of TS16 is
positive, but not sufficient to make TS16 conductive.
Maximum conductivity of TS17, short circuit of
the motor driven: the motor driven brakes maximal.
Minimum diameter of the ree! on the motor driven
The reel to be rewound has the maximum diameter.
The pulling motor runs at minimum speed.
The voltage flowing through motor and R59 is
maximal. The voitage on the emitter of TS16 is
positive, consequently,
maximum
conductivity of
TS16. Minimum conductivity of TS17: the motor
pulled brakes with a minimum force.
R60 limits the variations in winding time when the
mains voltage varies. When the mains voltage is
high, the base of TS16 becomes
more positive and,
thus, TS16 less conductive. To control TS17, the
voltage through R59 should be greater.
The interference pulses from the motor pulled are
short circuited by C58.
Electrical
brake
When the STOP or PAUSE
position is reached, (all
keys are released mechanically), the braking magnet
RE2 will be dead and tend to drop off.
The base TS15 becomes negative in respect of the
emitter: TS15 conducts. A positive voltage is
applied to the base of TS11. The motor driven by
the tape, generates a negative voltage, so that
the base of TS11
is positive towards the emitter:
TS11 conducts. A voltage begins to flow through
the motors, for the greater part through the motor
driven, because it works as a generator. The load
current through the generator will strongly brake the
tape transport.
As long as the motor driven generates a voltage
sufficiently negative to keep TS11 conductive, the
voltage through R61 will cause a voltage drop
across R304. As a result, TS19 will conduct.
Thus, a voltage is applied to the braking magnet,
which
is smaller than the mains voltage A (through
D22), but sufficient to prevent the braking magnet
from being de-energized. Moreover,
also TS15
remains conductive because the base remains
negative
in respect of the emitter.
From the above, it follows that the brake operation
is mainly effected by the electrical brake.
The mechanical brake is an auxiliary brake:
- When the mains voltage drops off and
- When the tape is inserted.
Delay circuit
The delay circuit prevents breakage of the tape or
tape loops to occur when the recorder is switched
over from REW or WIND to the START
position.
When the set is in the REW or WIND position, C391
is charged (+ via R308, - via R394 and D391).
When
it is switched to the START
position, C391
via R392 and the base emitter diode of TS392
parallel to R393, are discharged. Now TS392 will
become conductive. When TS392 conducts, TS391
and TS9 will block. When after some time C391 is
sufficiently discharged, TS392 will block and,
consequently, TS391 wil! become conductive. The
base of TS9 now becomes negative in respect of
the emitter, so that TS9 conducts and the pressure
roller is attracted.
Automatic switch-off circuit
The recorder stops automatically at the end of the
tape. As long as the tape runs, TS6 is not conductive
so that the magnet RES is not excited. At the end of
the tape, the contact TC is closed by the metal
tape-leader, so that R79 gets earth potential. By a
negative pulse on the base of TS6, TS6 becomes
momentarily conductive and RE3 momentarily excited.
When RES@ is excited, all the keys are mechanically
released and the recorder is switched to the STOP
position. C53 prevents that TS6 remains conductive.
After breaking the contact TC, C53 is discharged
via R78.
Speed control of the capstan motor
A generator G3 is mechanically coupled to the motor
M3. The AC generated is supplied to the cathode of
the diode D207 (The frequency of this AC depends
on the speed of the motor).
D207 allows only the negative half of the AC voltage
to flow through. The AC voltage of the generator
is converted to a square-wave voltage by TS204.
This square-wave voltage is differentiated by the
capacitor C203 (voltage through C203).
The voltage is rectified by the diodes D204 and
D205 and smoothed by the capacitor C204. The
smoothed positive voltage is applied to the base of
TS203. Also, via one of the speed adjustment
resistors,
a DC voltage is applied to the base of
TS203. The resultant of these two voltages determines
the measure of conductivity of TS203. When the
generator supplies less pulses, the resultant of
these voltages will te tower so that the conductivity
of TS203
increases. TS203 controls the base voltage
of TS202. The base current through TS201
is
controlled by TS202. The motor voltage is controlled
by TS201.
Diode D206 protects the transistor TS203 and the
capacitor C204 against too high a positive voltage.
The pulses, which remain after smoothing by C204,
are discharged by C206. C207 and R209 form a
filter effecting the stability of the control circuit.
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