Circuit Description—Type 422 AC-DC
(X I0 MAG switch pulled out). Variable capacitor C537
provides high-frequency compensation for a linear display
(XI operation) at fast sweep rates. When the X I0 MAG
switch is pulled out, resistive feedback is provided only
through R527 and capacitive feedback through C527-C528.
The feedback for X I0 operation is about 1/1 Oth that for
XI operation so the circuit gain is increased 10 times. Vari
able capacitor C527 provides high-frequency compensation
for a linear X I0 magnified display at fast sweep rates.
Paraphase Output Amplifier
The output signal from the Feedback Amplifier is con
nected to the base of Q544. Transistors Q544 and Q554 are
connected as a paraphase amplifier to convert the single-
ended input to a push-pull output signal which is necessary
to drive the horizontal deflection plates of the CRT. Circuit
operation is as follows: The positive-going sawtooth from
the Sweep Generator (or positive-going external horizontal
signal) is amplified and inverted through the Feedback
Amplifier stage to provide a negative-going signal at the
base of Q544. This negative-going signal at the base of
Q544 reduces its conduction and its collector goes positive.
This produces a positive-going sawtooth output signal at the
collector of Q544 which is connected to the right deflec
tion plate of the CRT.
Transistor Q560 is connected as a constant current
source for Q544-Q554 with its output current determined
by divider R564-R565 and emitter resistor R562. When the
current through Q544 is reduced, more current is available
to Q554 through C556-R556. This increase in current for
ward biases Q554, which is connected as a common-base
stage. The increase in current through Q554 produces a
negative-going sawtooth at its collector which is connected
to the left deflection plate of the CRT. Thus the single
ended input signal has been amplified and is available as a
push-pull output signal.
CALIBRATOR AND REGULATORS
General
The Calibrator and Regulators circuit provides a square-
wave output with accurate amplitude. This output is avail
able at the CALIBRATOR jack on the front panel or it is
internally connected to the vertical deflection system in the
CALIBRATE 4 DIVISIONS positions of both VOLTS/DIV
switches. This circuit also contains two regulator circuits to
provide regulated outputs of +10.5 and —81 volts. In addi
tion, this circuit provides the interconnections between the
power supply unit and the indicator and includes the volt
age sources for the VARIABLE control UNCAL lights. Fig.
3-10 shows a detailed block diagram of the Calibrator and
Regulators circuit. A schematic of this circuit is shown on
diagram 10 at the back of this manual.
Calibrator
Transistors Q765 and Q775 are connected as an astable
multivibrator. Frequency of operation is about one kilo-
hertz. Circuit operation is as follows: Assume that Q765
has just turned off and Q775 turned on. While Q765 was
on, C760 charged negatively on the Q765 side to a level
which is about 0.6 volt more positive than the emitter level
of Q765. Now with Q765 off, C760 discharges toward +12
volts through R760. As C760 discharges, the anode of
D760 follows and when it reaches a level about 1.2 volts
more positive than the base level of Q765 (as established by
divider R765-R773), Q765 is forward biased. As Q765
turns on, its collector rises positive and pulls the base of
Q775 positive through R763. Q775 turns off and its col
lector drops negative to about —6.5 volts to reverse bias
D780. With D780 reverse biased, the voltage across output
divider R786-R787 is determined by the voltage applied to
it through D782 from R780-R781 and the -8 1 -volt supply.
Calibrator Amplitude adjustment R780 is adjusted to pro
vide an accurate two-volt peak-to-peak square-wave signal at
the CALIBRATOR jack on the front panel. This also pro-
+ 55 V
+ 10.5 Volt
Regulator
Q714 Q 717
D714
+ 10.5 V
-no v
— 81-Volt
Regulator
Q734 Q737
D739 V739
------
— 81 V
Calibrator
Multivibrator
Q765 Q775
<
2 VOLT PROBE
CALIBRATOR
R786
1
R787
Calibrator signal
* to Channel 1 and
Channel 2 Input
Amplifiers
m 3-17
Fig. 3-10. Calibrator and Regulators detailed block diagram.
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