
Circuit Description—Type 324
combination of R340 and R342 switches D303 to its high
voltage state, turning Q305 on. Unblanking occurs, but dis
connecting the timing resistor and the timing capacitor pre
vents a sweep from being generated. The intensity should
be turned down under this condition to provide optimum
viewing and to conserve operating power, thereby leng
thening the operating cycle during internal battery powered
operation.
H O R IZO N TA L A M P LIFIE R < 6 >
General
The Horizontal Am plifier accepts a horizontal sweep
voltage from the Sweep Generator, amplifies it and applies
the resulting push-pull signal to the horizontal deflection
plates of the cathode-ray tube. During E X T H O R IZ opera
tion, the input from the Sweep Generator is disconnected,
allowing E X T H O R IZ input signals to be amplified and
applied to the horizontal deflection plates. The overall gain
of the amplifier is normally about 60 (Push-pull out
-single-ended input) and increases by a factor of 5 during
X5 H O R IZ MAG operation.
Block Diagram Description
Refer to the block diagram on the Horizontal Amplifier
schematic page. The horizontal sweep signal received from
the Sweep Generator passes through a horizontal gain cali
brating resistor, is processed by the Isolation Am plifier and
is amplified by the Output Amplifier. The amplified signal
is then applied to the left deflection plate of the cathode-
ray tube. The Output Am plifier is an operational amplifier
which uses R403-R404 as Rjn during X1 gain operation,
and R401-R402 during X 5 operation. The Isolation Am pli
fier is a common base amplifier, isolating the input circuit
from the Output Amplifier.
The signal from the Output Am plifier also drives the
Output Inverter, which supplies the signal to the right de
flection plate. The Output Inverter is also an operational
amplifier and has a gain of one under all operating condi
tions.
The Output Am plifier and Output Inverter circuits both
have current control circuits associated with them to pro
vide the additional current required during retrace time and
fast sweep operation.
The quiescent beam position (and therefore the hori
zontal area through which the beam moves) can be selected
by the POSITION control, and it is normally set to start the
sweep at the first vertical mark at the left of the graticule.
During X5 H O R IZ MAG operation, the POSITION control
range permits any 20% of the normal sweep to be presented
as a 10 division sweep.
When E X T H O R IZ operation is selected by the T IM E /
D IV switch, the Horizontal Am plifier circuit operates
exactly as previously explained, except that the sweep sig
nal from the Sweep Generator circuit has been replaced by
an externally applied signal. When the E X T H O R IZ VA R
control is fully clockwise, R334B is bypassed. The external
horizontal gain will decrease to 1/10 of its previous value
when the control is rotated fully counterclockwise.
Output Amplifier and Output Inverter
Refer to the schematic, and assume that a positive-going
sweep signal is arriving at the input of the amplifier. The
positive-going signal is felt at the emitter of Q 440, increas
ing the Q 440 collector current. The positive-going collector
voltage is felt at the base of Q 451. Q451 and Q 453 form a
non-inverting amplifier circuit, and a positive signal is
developed at the Q453 collector. This signal is amplified
and inverted by Q457, providing a negative-going signal for
the left deflection plate. The collector voltage of Q457 is
also applied to feedback circuit R452-C452. The changing
collector voltage of Q457 causes most of the signal current
re q u ire d
by the input signal to flow through the
R452-C452 network. Therefore, only a very small part of
the input signal is felt at the base of Q451 and at the
emitter of Q440.
The gain of the Output Am plifier is determined princi
pally by the ratio of feedback resistor R452 to the input
resistance of R403-R404. This is equal to approximately 30
during X1 gain conditions. When X5 gain has been selected,
the input resistance is decreased to approximately 1/5 of its
previous value, resulting in a circuit gain of approximately
150.
The voltage at the collector of Q457 is also applied
through R470 to the Q470-Q 473 Output Inverter circuit.
This circuit is also an operational amplifier, with the feed
back resistor (R471) equal to the input resistor (R470).
Gain of the circuit is therefore equal to one, providing an
equal but opposite polarity signal to the right deflection
plate.
It is desirable that the center two divisions of X1 display
be presented as a 10 division display during X 5 G A IN oper
ation. Potentiometers R438 and R432 permit the circuit
current to be adjusted as necessary to permit this situation
to occur.
The current flowing through the summing node at the
emitter of Q 440 determines the circuit output voltages, and
therefore, the beam position. The POSITION control
modifies this summing node current by using a dual poten
tiometer arrangement for coarse and fine positioning. The
fine potentiometer (R 421) has its pickoff voltage con
nected through a large resistor and through Power Ampli-
3-12
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