Tektronix 585 - Page 37

Circuit Description — Type 585
DISCONNECT
DIODES
V152
SWEEP GATING
MULTIVIBRATOR —
V135 V145
SAWTOOTH
GENERATOR -*• TO HORIZONTAL
V161 V173 AMPLIFIER
+ GATE C.F.
---------- + GATE A
VI 93 A
UNBLANKING
C.F.
V183B
HOLDOFF C.F. ’ s
V183A V133B
DELAYED DELAYED TRIGGER LOCKOUT
AMPLIFIER -*■ MULTIVIBRATOR SAWTOOTH C.F. _ SAWTOOTH A
TRIGGER vil4 V125 V139A V193B
fig. 4-7. Time Base Generator A block Diagram.
can be individually connected to the input of the Time-Base
B Trigger circuit. The operation of the Trigger Amplifier
and Trigger Regenerator is essentially identical with other
Tektronix delaying sweep oscilloscopes.
An amplified triggering signal from the Trigger Amplifier,
V74A and V74B, is applied to the Trigger Regenerator
multivibrator. The Trigger Regenerator is a monostable
Schmitt circuit which switches when the output of the trigger
difference amplifier reaches a certain level. When the multi 
vibrator switches, a negative output pulse is applied to the
B' Sweep Gating multivibrator to initiate a sweep. The
pulse is relatively constant in amplitude regardless of the
original triggering signal amplitude. After application of the
pulse to the sweep circuit, the trigger regenerator resets to
await the next triggering signal.
The TRIG. LEVEL CENTER control, R78, permits an adjust 
ment of the output voltage level of the Trigger Amplifier.
This assures that the Trigger Amplifier output signal will lie
in the center of the Trigger Regenerator input hysteresis volt 
age range when the Trigger Amplifier grids are both zero
volts to ground.
TIME-BASE GENERATOR A
General
The Time-Base Generator A block diagram of Figure 4-7,
and the Time-Base Generator A diagram at the back of
this manual should be used during the following discussion.
The output pulses from the A Trigger Regenerator system
previously discussed are applied to the grid of V135A, the
input triode of the Sweep-Gating Multivibrator V135A,
V135B and V145. The Sweep-Gating Multivibrator is a
Schmitt Gating circuit acting as an electronic switch for the
Time-Base Generator circuit. When the negative triggering
pulse is received, the Sweep-Gating Multivibrator switches,
cutting off the Disconnect Diodes V152A and B and allow 
ing the Miller-Runup sweep generator circuit to operate.
A positive going square wave output of the Sweep-Gating
Multivibrator is taken from the cathode of V135B and is
connected through the Unblanking Cathode Follower V183B
to the c rt to unblank the tube. The unblanking signal is
employed only in the INTERNAL SWEEP and SINGLE SWEEP
positions of the HORIZONTAL DISPLAY switch. Another
positive going square wave output of the Sweep-Gating
Multivibrator is connected through the +Gate Output
Cathode Follower V193A to the +GATE OUT connector on
the front panel.
The sawtooth voltage used by the Horizontal Amplifier
to move the c rt electron beam across the face of the c rt
is also available at the front panel at the SAWTOOTH A
terminal. Cathode follower V193B isolates the internal
sawtooth voltage circuit from external loading. Maximum
external load of 18K is permissible.
For persons experienced with Tektronix time-base gener
ator systems, the Type 585 Time-Base Generators are nearly
identical with those found in any of the 530 or 540 series
instruments. The major difference is that the Type 585 Time
Base A Miller Runup circuit fastest rate of rise has been
increased by a factor of 2. This requires doubling the
static current of V 1 61 and slightly altering the associated
circuitry.
DIFFERENTIATING
FROM TRIGGER — ► CIRCUIT
CIRCUIT