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3.1.6
Delayed time base triggering
To initiate sweeps, trigger signals can be derived from the A and B vertical channel preamplifiers, or from an
external source as selected by the trigger source push button switch.
With both the A and B pushbuttons depressed simultaneously, composite triggering is derived from the delay -
line driver stage of the Y amplifier channel. AC and DC coupling is provided to the impedance converter. The
polarity of the trigger signal, negative or positive-going, on which the display will start, is determined by
changing the output polarity of the impedance converter by the SLOPE switch.
With MTB selected, the delayed time base starts directly after the delay time. The DELAY TIME control in
conjunction with the comparator determines the delay time for the delayed time base generator.
3.1.7
Delayed time base circuit
The delayed time base is operative unless its TIME/DIV switch is in the OFF position. It starts immediately
after the delay time, or upon receipt of the first trigger pulse after the delay time.
The sawtooth signal derived from the main time base sweep generator is passed to a comparator where it is
compared with an accurately adjustable d.c. voltage, controlled by the DELAY TIME control.
The comparator output is pulse-shaped and provides the required delay pulse for the sweep-gating logic of the
delayed time base generator. A sawtooth voltage is then initiated.
The delayed sweep is reset by the hold-off circuit of the delayed time base (end of the sweep detection) or by
the main time base.
It can be started again by the output signal of the comparator after the initiation of the next main time base
sweep.
When pushbutton MTB of the horizontal deflection mode controls is selected, the part of the trace coinciding
with the delayed sweep is intensified.
3.1.8
Alternate time base logic
In ALT TB mode an electronic switch enables main time base display and delayed time base display to be
alternately traced on the screen.
The two displays can be separated by varying the voltage applied to the vertical amplifier, derived from the
driving circuits of the electronic switch. This separation is symmetrically variable by means of the TRACE
SEPARATION control on the front panel.
In the ALT TB mode the vertical channel multivibrator is controlled by a signal derived from the electronic
switch.
In the vertical and horizontal ALT modes, successively are displayed on the screen, Channel A and main
time base, Channel A and delayed time base, Channel B and main time base, Channel B and delayed time base.
3.1.9
Power supply
The mains (line) supply is transformed and rectified before being applied to a d.c. to a.c. regulator.
When the instrument is operated from a battery supply, the battery output is connected directly to the d.c.
to a.c. regulator.
The output of the regulator is coupled to a transformer and rectifier which, after rectification, provides the
—1.5 kV potential and the circuit supply lines. The —1.5 kV is also multiplied to 8.5 kV to supply the required
total accelerating voltage of ~ 10 kV.
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