Tektronix 516 series, Instruction Manual

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TIME-BASE GENERATOR
The Time-Base Generator, upon receipt of a negative trig­
ger pulse from the Time-Base Trigger, produces a linearly
rising (sawtooth) voltage which is applied through the Hori­
zontal Amplifier to the crt horizontal deflection plates. This
causes the spot to move from left to right on the crt screen
and form the trace. The amplitude of the sawtooth voltage
is about 150 volts. Its rate of rise is controlled by the values
of the Timing Capacitor and Timing Resistor switched into
the circuit by the TIME/DIV. control on the front panel.
The Time-Base Generator consists of three main circuits;
the Sweep-Gating Multivibrator, the Miller Runup Circuit, and
the Hold-Off Circuit. The Sweep-Gating Multivibrator con­
sists of V135A, V135B, and V145A. The essential components
of the Miller Runup Circuit are: The Miller Runup Tube,
V I61 A; the Runup Cathode Follower, V161B; the Disconnect
Diodes, V152A and V152B; the Timing Capacitor, C160; and
Circuit Description — Type 5 1 6
the Timing Resistor, R160. The Hold-Off Circuit consists of
the Hold-Off Cathode Followers, V183A and V183B; the
Hold-Off Capacitor, Cl 80; and the Hold-Off Resistors, R180A
and R180B. Also considered a part of the Time-Base Genera­
tor are the Unblanking Cathode Follower, V145B, the +
Gate-Out Cathode Follower, V193A, and the Sawtooth Out
Cathode Follower, V193B.
A block diagram of the Time-Base Generator is shown in
Fig. 4-5.
Sweep Generation
In the quiescent state—that is, when no sweep is being
generated— V135A is conducting and V145A is cut off. (The
STABILITY control, R110, or the PRESET STABILITY adjustment,
R ill, whichever'is in the circuit, is set so that the grid of
V135A is just above cutoff voltage.) The plate of V145A is
4-7
Fig. 4 -5 . Time-Base G enerator block diagram .