Generation Of The Delayed Trigger Pulse - Philips PM 3347 Manual

14
conductive. When the anode-voltage of B14, applied
to the grid of B 17', rises above the switching level of
the Schmitt trigger, the circuit switches over: B 17'
conductive and B 17" cut-off. The anode voltage of
B17" therefore rises abruptly.
When the ramp-voltage drops below the cut-off level
of B13 (during the fly-back interval) the anode volt-
age of B 17" returns to the quiescent value.
Thus a rectangular voltage wave-form is produced at
the anode of B 17".
This voltage waveform is differentiated by capacitor
C59 and resistor R143//R144, so that positive and
negative spikes appear at the grid of trigger-amplifier
valve B 16t.
With no input signal present, B16t is biased beyond
cut-off and the positive spikes cause it to become
conductive, thus producing positive output spikes at
the cathode.
The negative spikes theoretically do not appear at
the output; however, some effect may be evident in
the output signal, see Fig. 11.
Thus, after time base B has been triggered, there
follows a certain pre-determined time-delay before
time base A can operate. The trigger pulse is also
available at the socket "DELAYED TRIGG.". This
delay can be set with controls "DELAY - TIME or
TIME/cm" and "DELAY TIME MULTIPLIER
1-10" and the actual time interval is the product of
these two settings.
T= ~Time~cm setting X ~~Delay time multiplier~~setting
V/B 13
g
200V
814a
330 V
817 a
r
T
~ tugger
point
B16t g -~
B 16 t c --~
Fig. 11. Generation of the delayed trigger pulse
BT3 14 Cathode level
set bid R 4
Schmitt trigger
switching level
Output of Schmit!
trigger
Differentiated rectangular
waveform
Output at Socket
"Deli D
trigger"
PEM 2895