Tektronix 3B2 TIME-BASE Instruction Manual page 11

CIRCUIT DESCRIPTION
A block diagram of the Type 3B2 is shown in Fig. 4-1.
Delay Generator, Sweep Generator, and a Clock Pulse
the Trigger Generator can be triggered with a very slowly
changing dc level. The two AC positions of SW5 block the
de and very low-frequency ac components of the trigger
signal. The AC FAST position uses a high-pass network to
trigger on only the high-frequency component of a signal
that contains both high and low frequencies.
V13 is a cathode follower that isolates the input from
the remaining sweep trigger circuitry. B10 is a neon lamp
that protects V13 from excessive input voltage. The output
and then to sweep trigger comparator Q24 and Q34. The
position of SLOPE switch SW19 determines the connections
the circuit responds to the negative- or positive-going por-
tion of the input signal.
cuit, and an adjustable de voltage (set by the LEVEL con-
input, Q34 is turned off. When the signal input reaches
a value in excess of the value set by the LEVEL control,
Q34 turns on and switches D35 rapidly to its high-voltage
To understand the operation of the comparator circuit,
assume that the SLOPE switch is set at + and the LEVEL
control is set for about +4 volts. This places +4 volts on
the base of Q24, With no input signal present, the base of
age conditions Q34 will be turned on, and @Q24 will be
turned off. Q34 turns off when the incoming signal arrives
at its base and becomes more positive than the +4 volts
circuit.
DELAY GENERATOR
The Delay Generator consists of a gated multivibrator
delayed-trigger generator. The delay generator circuit is
generator when the SWEEP DELAY switch is set to OUT.
Incoming pulses from the Trigger Generator are coupled
to the gated multivibrator through T51. The multivibrator is
The output of the multivibrator (collector of Q64) is a nega-
ing and its collector voltage is high. The incoming pulse