Section IV Model 185B
Paragraphs 4-85 to 4-100
4-85. OUTPUT. The output of unity amplifier V201A- shock-excited into 50-mc oscillation. Q603 overcomes
Q210 is fed: the tank-circuit losses, resulting in a constant-am-
a. To one side of the comparator (see paragraph plitude oscillation, and a 50-mc voltage is coupled to
5602, the 50-mc connector. When the sync pulse ends,
4-61). The path from unity amplifier is through R286, CR605 is again clamped to a negative voltage, termi-
the time scale VERNIER (or, when TIME SCALEver- nating the 50-mc oscillation.
nier is at CAL, through contacts on switch S204),
through Sweep Calib adjustment R285, TIME SCALE
MAGNIFIER switch S201 where the staircase voltage 4-94. DC CALIBRATOR VOLTAGES. The rest of
is attenuated if S201 is on any except the X1 setting, this circuit is simply a dc voltage divider, between
-12.6 volts and ground. The level of the voltage fed
and cathode follower V201B. to the AMPLITUDE DC OPEN CIRCUIT connector de-
pends on the setting of S601, the CALIBRATOR AND
b. To the grid of V501B in horizontal amplifier SYNC PULSE switch.
assembly A501.
4-86. HORIZONTAL AMPLIFIER. The horizontal
4-95. VERTICAL AMPLIFIER.
amplifier is a conventional, single-stage differential
amplifier. The scan voltage is applied to one half of 4-96. GENERAL OPERATION.
the amplifier, the horizontal positioning voltage to 4-97. Figure 4-11 is a block diagram of the vertical
the other. The level of the positioning voltage is set
with R509, the HORIZONTAL POSITION control. The amplifier. The signal under investigation is applied
output of the amplifier is connected directly to the to the input of the vertical plug-in unit, and is applied
horizontal deflection plates of the crt. to Model 185B vertical amplifier via pins on connector
J1 (not shown in figure 4-11).
4-87. CALIBRATOR. 4-98. In the Model 185B vertical amplifier, input
4-88. SYNC PULSE. When CALIBRATOR ANDSYNC signals are applied to cathode followers V1 and/or
PULSE is full counterclockwise, pulse amplifier Q60l V2, and then to differential amplifiers Ql-Q2 and
is biased so that it can conduct when triggered with a Q3-Q4. Multivibrator V4 controls the differential
negative pulse. When the ramp-gate pulse (paragraph amplifiers so that only one is turned on at a time.
4-40, step c) appears on its base, Q60l saturates, Thus only the signal applied to the ?on? differential
and its collector rises to +12 volts. amplifier is amplified and applied to the crt. The
?off? differential amplifier blocks the signal applied
4-89. As Q60l turns on, Q602 is driven into satur- to it, Circuits in the vertical plug-in unit control
ation. Capacitor C602 charges slowly through R604 multivibrator V4.
and Q601, holding Q60l on for a time determined by
R604-C602 time constant.
4-99. CONTROL OF DIFFERENTIAL AMPLIFIERS.
Except while switching, one plate of multivibrator V4
4-90. Before ramp-gate pulse appeared on base of is positive and the other negative; for purposes of
Q601, CR604 was conducting and therefore presented explanation, assume the V4A plate is positive, and
a very low impedance. When positive pulse from
Q60l appears on its cathode, CR604 acts in a slightly therefore diode CR1 between the plate of V4A and the
different manner than an ordinary diode. Instead of bases of Ql-Q2 is conducting. Under this condition,
immediately cutting off, reverse current flows mo- the positive voltage on the V4A plate is applied to the
bases of Ql-Q2, back-biasing their emitter-base
mentarily, and the impedance of the diode remains junctions, and Ql-Q2 are cut off. At the same time,
low (the reverse current is supported by the carriers the V4B plate is negative, back-biasing diode CR2 be-
stored during the time the Q60l collector is rising to
+12 volts). Carriers are depleted abruptly, current tween V4B and Q3-Q4, and amplifier Q3-Q4 operates
stops, and impedance of diode CR604 rises sharply; normally.
because of this characteristic, diode CR604 provides
very fast switching action, and the result is a fast- 4-100. CONTROL OF MULTIVIBRATOR V4. When
rise pulse. During the short period between back- the plug-in unit is the Model 187B Dual Trace Ampli-
bias and cut-off, CR204 produces a small voltage fier, the vertical presentation switch (channel and
step; diode CR603 blocks this step, and passes only mode-of-operation selector) controls multivibrator
the steep-rise portion of the pulse. V4. The vertical presentation switch lock multivi-
brator V4 in one state or the other to provide single-
4-91. The pulse, thus shaped by CR604 and CR603, channel operation, or allows multivibrator V4 to free-
is coupled to J601, SYNC PULSE OUTPUT connector. run to provide dual channel operation. Multivibrator
V4 is designed to free-run up to about 180 kc, so in
4-92. PULSED 50-MC AMPLIFIER. During the time dual channel operation, both differential amplifiers
between pulses from amplifier Q601, the junction of are turned on some time during each sampling period
?260?7 and R610 is slightly negative and CR605 conducts, even when the instrument is running at its maximum
holding base of Q603 slightly negative. sampling rate of 100 kc. To provide a differential
display, the Model 187B simultaneously applies the
4-93. When amplified ramp-gate pulse appears on Channel A signal to the Model 185B amplifier V1A and
Q60l collector, CR605 (a diode of the same type as the Channel B signal to amplifier VlB, Vertical de-
described in paragraph 4-90) becomes back-biased. flection on the crt is then proportional to the differ-
When it snaps off, resonant circuit T601-C610 is ence between the signal voltages.
4-12 01255-1 |
ACEC
HEWLETT-PACKARD
