Tektronix T PLUG-IN Instruction Manual page 17

C160 charges linearly, and the voltage at the
cathode of the RunupC.F, V8110A rises linearly.
Any departure from a linear rise in the voltage
at this point will produce a change inthe voltage
at the grid of the Miller Tube i n such a direction
The linear rise in the voltage at the cathode
tooth, or Time-Base. Timing Capacitor C160
and Timing Resistor R160 are selected by means
of the TIME/DIV. switch (SW160). The Timing
Resistor determines the current that charges
the Timing Capacitor. By means of the TIME/
DIV. switch, both the size of the capacitor being
charged and the current charging the capacitor
can be selected to cover a wide range of saw-
tooth slopes (time-bases). For high-rate time
bases the bootstrap capacitor, C8140, helps
supply the current to charge the stray capaci-
tance at the plate of the Miller Tube which
permits the plate voltage to rise at the required
If uncalibrated time-bases are desired, the
VARIABLE TIME/DIV. control may be turned
away from the calibrated position. This control,
R8320, varies the time-base rate from approxi-
mately 5 SEC/DIV. to .2 uSEC/DIV. Switch
SW8300 is ganged with the variable control in
such a way that the UNCALIBRATED light
comes on when the control is turned away
from the CALIBRATED position.
As explained previously, the time-base rate
{the rate at which the spot moves across the
face of the crt) is determined by the timing
circuit components, C160 and R160. The length
of the time-base (the distance the spot moves
across the face of the crt), however, is
determined by the setting of the Sweep Length/
Sawtooth Amplitude control, R8260. As the
time-base voltage rises linearly at the cathode
of V81l10A, there will be a linear rise in
voltage at the arm of the Sweep Length/Saw-
tooth Amplitude control R8260. This will
increase the voltage at the grid and cathode
of V7530A, and at the grid and cathode of V7530B.
As the voltage at the cathode of V7530B rises,
the voltage at the grid of V7650B will rise.
When the voltage at this point is sufficient to
bring V7650B out of cutoff, the multivibrator
sweep portion, and the plate of the Miller Tube
base sawtooth, during which time the crt beam
The holdoff circuit prevents the Time-Base
Generator from being triggered during the
retrace interval. That is, the hold-off allows
a finite time for the Time Base circuits to regain
a state of equilibrium after the completion of
the sawtooth,
During the trace portion of the sawtooth the
Hold-Off Capacitor C180 charges through
V7530A, as a result of the rise in voltage at
the cathode of V7580A. Atthe same time, the grid
of V7650B is being pulled up, through the Hold-
Off C.F. V7650B, until V7650B comes out of
cut-off and starts conducting. As mentioned
previously, this is the action that initiates the
retrace. At the start of the retrace interval
C180 starts discharging through the Hold-Off
Resistor. The time constant of this circuit is
long enough, however, so that during the retrace
interval, (and for a short period of time after
the completion of the retrace) V7530B holds
the grid of V7650B high enough so that it
cannot be triggered. However, when C180 dis-
charges to the point that V7530B is cutoff,
Stability Controls