Tektronix 7B51 Instruction Manual page 32

+15 V
+15V
SLOPE
R234
-15V
r t - - -
LEVE L
R221
-15V
Circuit Description-Type 7851
+15 V
LEVEL/SLOPE
Control
OI~O~-
Positive Slope
+50 V
R269
•
[
7T
Fig. 3·4. Trigger Path for Positive Slope Triggering (simplified).
the result is the opposite of the above and produces a CRT
display which starts at a more negative point along the +
slope of the trigger signal.
The slope of the input signal which triggers the sweep is
determined by the SLOPE switch, S260. When the SLOPE
switch is set to the + position the collector of 0244 is con-
nected to the +15 volt supply through CR245. This reverse-
biases CR246 and holds 0260 cut off. With 0260 cut off,
CR255 is reverse-biased. Now the collector current of 0254
must flow through CR256 and the parallel combination of
®
CR262 and R267-C267-L267 to the +15 volt supply. Since
the output pulse from the Trigger Generator circuit is de-
rived from the negative-going portion of the signal applied
to the Trigger TO Stage, the sweep is triggered on the
positive-going edge of the input signal.
With the SLOPE switch set to -, conditions are reversed
(see Fig. 3-5). The collector of 0254 is connected to the
+15 volt supply through CR255 and 0260. CR245 and
CR256 are reverse-biased and the collector current from
0244 is diverted through the Trigger TO Stage. The signal
applied to the Trigger TO Stage is now in phase with the
3-5
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