vertical deflection plates in the CRT. This last pair of amplifiers also uses a compensating network (part of the common
from going to the blanking multivibrator. This causes the blanking multivibrator to function as a free-running instead of a
emitter circuit) to improve the frequency response.
monostable multivibrator. As such, the blanking multivibrator generates negative pulses at a rate of 60 kc. This means that
the electronic switch circuit is triggered at this rate, and that the channel A and B amplifiers are being alternately activated
b. Notice that a portion of the output signal from amplifiers Q9408 and Q9409 is fed bac k to a network consisting of
(approximately 6 microseconds on the approximately 9 microseconds off.
R9255, R9254, R9256, R9261, and C9218. After passing through this network, the signal is applied to Q9400 and Q9401 of
the Darlington emitter followers. Feeding back a portion of the output serves to improve the frequency response of the circuit.
e. Channel A + Channel B. Setting the MODE switch to A + B deactivates electronic switch Q9600, Q9601 by removing
the B+ voltage. This activates the channel A and channel B amplifiers simultaneously so that the resultant output (channel A
+ channel B). You will notice that diodes CR9202 (zone A9) and CR9203 (zone B9) are no longer reverse-biased, and
Section III.1. FUNCTIONAL THEORY - DUAL TRACE PLUG-IN
therefore, the loading of one channel by the other reduces the overall bandwidth of the system.
79-02A AND CRT TERMINATION NETWORK (MAIN FRAME)
Delay Line Drivers
The output of both the channel A and channel B amplifiers is applied to delay line drivers Q9400, Q9401, Q9402, and Q9403
Two almost identical preamplifiers (CH1 and CH2) are provided. Since these units are nearly identical, only one unit is
(Darlington emitter followers). After passing through the delay line drivers, the signal is applied to a balanced, distributed-
discussed and the other is compared.
bifilar-helical, delay line. When the oscilloscope is set up for internal triggering, the delay line provides the necessary time
delay (230 nanoseconds) so that the leading edge of the signal, which triggers the delaying sweep plug-in, can be viewed with
. Input Coupling. Input connector
J1 for channel 1(A1) offers
an input impedance
of 1 megohm and
the base line. Networks Z9401, R9413, and Z9402, R9414 provide the proper termination for the delay line, and also
the applied signal. The signal applied to J1 may be directly coupled through R1, capacitively coupled through C1, or the input
compensate for the input capacitance of emitter followers Q9413 and Q9414. By adjusting DELAY LINE TERM ADJUST
to the instrument may be grounded, as established by the DC-AC-GND switch. The selected signal is first applied to a
resistor R3 (zone A10), we can be sure of obtaining a proper termination.
capacitive-resistive network which comprises a frequency-compensated voltage divider. The particular attenuator used is
selected by VOLT/DIV switch S902. In the 20 position of this switch, they Y plate of C2 is connected through S902-4, while
Trigger Pick-off Circuit
R8, R9, C11, and C19 are connected through S902-3 (input) and S902-2 (output). In the 20 position of this switch, the Y plate
of C2 is connected through S902-4, while R8, R9, C11, and C19 are connected through S902-3 (input) and S902-2 (output).
a. Notice that a portion of the output from the delay line drivers goes to trigger pick-off amplifiers Q9501 and Q9502
R8 and R9 comprise a low frequency divider, C11 and C19 compromise a high frequency divider, and C2 acts as a trimmer.
(zone C10). These amplifiers convert the double-ended output of the delay line drives (push-pull signal) into a single-ended
C11 may be tuned for the desired frequency response. That portion of the signal which appears across R9 in parallel with
signal. After it is amplified and inverted by the trigger pick-off amplifiers, the signal goes through emitter follower Q9503 to the
C19 is coupled through S902-2 to the amplifier circuits. All the remaining switch positions introduce a similar divider. The 10
SOURCE switch in the delaying sweep plug-in. Amplifier Q9505 and TRIG DC LEVEL variable resistor R9503 provide the
volts through the 0.1 volt dividers, also have frequency adjustments (C12, C13, C14, C16, C17, and C18, respectively).
proper dc operating level for emitter follower Q9503.
b. Differential Amplifier. The input circuit for the amplifier section is differential V921 and V922 (B7). The VARIABLE
b. A portion of the output from the emitter follower Q9503 is also applied to amplifier Q9504. If at the same time
control on the front panel of the dual trace plug-in 79-02A adjusts the B+ on both sections of the differential amplifier. This
POSITION control R9234 (zone B8) is set so that the displayed signal appears on the CRT, Q9504 functions as a normal
control may be set to the detent (CAL) position, or to a position of less voltage. When the control is set to other than the CAL
class A amplifier. In this instance, the amplifier doesn't produce sufficient output voltage across either of the beam position
position, it closes a switch which completes the circuit to illuminate the UNCAL indicator. DC BAL (coarse and fine) controls
indicators (neon lamps DS9501 and DS9502) to cause them to illuminate.
are available to balance conduction of the differential amplifier, thus preventing depositioning of the trace as the VARIABLE
controls is operated. Gas compensation adjustment R201 is provided to neutralize the effect of any leakage currents in the
c. Let's see what happens when the POSITION control is set so that the signal is not displayed on the CRT (where the
differential amplifier. GAIN ADJ control R227, which sets the gain of the amplifier to a calibrated level, and invert balance
electron beam is directed below the bottom of the CRT screen). Under these conditions, amplifier Q9504 is cut off and the
control R231, which minimizes shifting of the trace when the position of the NORM-INVERT switch is changed, are provided.
voltage difference across lamp DS9502 exceeds its firing potential, causing them to illuminate.
c. Amplifiers . A series of amplifiers consisting of common-base amplifier Q201, common emitter amplifier Q204, and
d. However, if the POSITION control is set where the electron beam is directed above the top of the CRT screen,
emitter follower Q206 are complemented by Q202, Q203, and Q205, with the same configuration. These two series of
amplifier Q9504 is driven into saturation. This makes the voltage difference across lamp DS9501 high enough to cause it to
amplifiers, in conjunction with NORM-INVERT switch, compromise a push-pull amplifier circuit. The NORM-INVERT switch
illuminate. At the same time, lamp DS9502 is extinguished because there is practically no voltage difference across it.
(A9) makes it possible to cross-connect the amplifiers. With the switch in the NORM position, the signal from Q201 is applied
to Q203. The same relationship exists between exists between Q202 and Q203 or Q204. Thus, when the INVERT position of
Vertical Deflector Amplifier
the switch is selected, the transistor line-up is reversed. The POSITION control (A10) varies the bias on Q203 and Q204 to
deflect the trace vertically.
a. Passing through emitter followers Q9413 and Q9414, the double-ended output signal of the delay line is applied to
amplifiers Q9404 and Q9405. In the common emitter circuit of both amplifiers, a compensating network improves the
d. X10 Amplifier Section and Output Amplifier. The VARIABLE switch may be pulled out to increase the gain of the
frequency response of both stages. The amplified and inverted signal passes through two more emitter followers, Q9406 and
preamplifier by a factor of 10. In the normal (depressed) position of the switch, B+ is removed from the output stage of the
Q9407, to another pair of amplifiers, Q9408 and Q9409. These amplifiers amplify and invert the signal and pass it on to the