Tektronix 585 - Page 40

Circuit Description — Type 585
SWEEP STOPS
and rises to about + 105 volts to gate on the crt beam dur 
ing a sweep. The unblanking waveform goes directly to
the HORIZONTAL DISPLAY switch, and is connected to the
crt circuit in all positions except Time-Base B.
+ GATE A
The Sweep Gating Multivibrator positive gate waveform
used by the Unblanking C.F. is also used by the front panel
terminal +GATE A. The control grid of V193A rests at
about — 20 volts during periods of no sweep, and rises to
about + 20 volts during a sweep. The output waveform
therefore operates between ground and about + 20 to + 30
volts.
Fig. 4-8. Single-Sweep Waveform.
2. A ’ DEL ’ D BY ‘ B ’
When the HORIZONTAL DISPLAY switch is placed in the
A' DEL'D BY 'B' position, the Lockout Multivibrator, V125
and V133A, serves the same function as when the HORI 
ZONTAL DISPLAY switch is at ' A ' SINGLE SWEEP. However,
instead of the Lockout Multivibrator receiving the unlocking
pulse from the front panel RESET button, it receives the
pulse from the Delay Pickoff circuitry. A positive pulse of
about 5 to 7 volts is delivered to the grid of V 1 44 from the
Delay Pickoff circuit each time that Time-Base B generates
a sweep.
With the HORIZONTAL DISPLAY switch in the A' DEL'D
BY B' position, the Time-Base A sweep generator system
will be permitted to operate only during a sweep of the
Time-Base B sweep generator. The permission to operate
occurs at a time determined by the Time Base B TIME/CM
or DELAY TIME control multiplied by the setting of the
DELAY-TIME MULTIPLIER control. The actual operation is
determined by the STABILITY control, whether it is in a
triggerable or free-run state.
The crt display is that of the Time Base A sweep gener 
ator.
3. " ‘ B ’ INTENSIFIED BY ‘ A ’
When the HORIZONTAL DISPLAY switch is placed in the
B' INTENSIFIED BY A' position, the operation of the Lock 
out Multivibrator is identical with operation as in 'A' DEL'D
BY B'. However, the Horizontal Amplifier receives a differ 
ent signal.
The crt presentation is that of the Time-Base B sweep gen 
erator. If the Time-Base A sweep generator is caused to
generate a sweep, the sawtooth voltage is not seen on
the crt. Time-Base A presents only its crt unblanking signal
to the crt circuit to intensify the portion of the display where
the delayed action of Time-Base A occurs. (See Fig. 4-9).
Unblanking
The Sweep Gating Multivibrator provides a positive gate
pulse coincident with each sweep to unblank the cathode
ray tube. The output of the Unblanking Cathode Follower
V183B rests at about + 55 volts during periods of no sweep,
TIME-BASE GENERATOR B
Time-Base Generator B is very similar to Time-Base Gen 
erator A except its maximum sweep rate is not as fast and
it does not have the delayed sweep and single sweep cir 
cuitry.
The Sweep Gating Multivibrator, V235A, V235B and V245,
performs the same function as in Time-Base A. The Discon 
nect Diodes require less pull-down current of V245, therefore
the pentode serves adequately.
Time-Base Generator B has a closer tolerance linearity
specification of 0.1 % deviation from a true sawtooth output
waveform each 10% of its total change. This then requires
higher gain of the Miller Integrator (V261 ) than in Time-
Base A. The increased gain is accomplished by using a
higher plate load resistor for V261 . The grid of the Miller
Tube does not move more than about 0.4 volt during a
sweep. Thus the voltage gain of the Miller Integrator is
about 400.
The output sawtooth voltage of Time-Base Generator B
goes directly to the HORIZONTAL DISPLAY switch. The
Delay Pickoff circuit receives the ’ B ’ sawtooth in all posi 
tions except Time-Base A, and ‘ A ’ SINGLE SWEEP. The
Horizontal Amplifier receives the sawtooth in Time-Base B
and 'B' INTENSIFIED BY 'A' positions.
The Unblanking C.F. V293A output is connected directly
to the HORIZONTAL DISPLAY switch. The signal is coupled
to the crt circuit in the Time-Base B and B ’ INTENSIFIED BY
A ’ positions. The signal rests at about + 40 volts during
periods of no sweep, and rises to about + 90 volts to gate
the crt beam on during a sweep. Note that the Time-Base
B unblanking pulse amplitude is about 15 volts lower in
amplitude than the unblanking pulse of Time-Base A. This
difference permits the Time-Base A unblanking pulse to
brighten a part of the trace that indicates ' B ' INTENSIFIED
BY A ’ .
Alternate-Trace Sync A
Synchronizing pulses for alternate-trace plug-in preampli 
fiers are supplied via D 1 42 and the differentiating network
C 1 54-R1 54. Both positive and negative sharply differentiated
output pulses are applied from C154-R154 to the plug-in unit.
Only the positive pulses are used by the plug-in unit
alternate-trace switching circuitry.
4-10