I
Section IV Model 162B
Paragraphs 4-7 to 4-14
4-7. DIFFERENTIAL AMPLIFIER. Differential 4-11. CONSTANT CURRENT GENERATOR. The ac
amplifier VlO2A/B amplifies the signal from cathode signal is coupled to the output through C307 and C308,
follower VlOlA/B and converts it froma single-ended but the dc signal is reduced in level from +75 volts at
signal to the balanced signal necessary for the main the cathode of V103A to approximately zero volts at
vertical amplifier. In any operating mode other than the output. Referring to figure 4-4, thegrid of V303A
A-B, the grid of V102B is fixed at a dc level set by is biased by voltage divider R320-321 to -32 volts.
cathode follower VlOlB. When a signal appears at the This fixed bias, along with cathode bias resistor R318,
grid of V102A it is amplified and appears as a signal regulates the tube at a constant plate current. Since
at the plate. At the same time a signal appears at V303A draws constant current through R310, an
the cathode of V102A. Since the cathodes of the two increase in dc level will not change the drop across
halves of V102 are tied together this signal appears R310 and the dc signal will appear at the output un-
between the cathode and gridofVlO2B. This differen- attenuated. Positive feedback from the input through
tial signal is also amplified and appears at the plate R312 compensates for the voltage division by I1308
of V102B as a signal opposite in polarityto the signal and the 1 megohm resistor in the input of the main
on the plate of V102A. In the A-B mode, the signal vertical amplifier. R308 isolates the output from the
from the ChannelAattenuator is switched toVlO2A and capacitance of V303A.
the signal from the channel B attenuator is switched
to V102B. The operation of the differential amplifier 4-12. Vert. Pos. Adj. R319 acts as a coarse vertical
in this mode is similar to that described above: a position control and allows centering of the range of
signal appears at the grid of V102A and is amplified; VERTICAL POSITION control R127-128. Potenti-
the same signal appears at the cathode, but since ometer R19 adjusts the cathode voltage of V303A and
another signal now appears at the grid of V102B only thereby adjusts the dc level at the plate of V303A,
the difference signal between channel A and channel B resulting in the same effect as adjustment of R127-128.
is amplified. Therefore, any signal which appears at
both grids with the same phase and amplitude (common
mode) will not appear in the output.
4-13. ELECTRONIC SWITCH.
4-14. The output of each channel is controlled by
4-8. With VERNIER control R123 in CALIBRATED switching multivibrator V302, shown in figure 4-5.
the cathode of V102A and V102B are tied together. When V302A conducts, its plate voltage is approxi-
When R123 is rotated out of the CALIBRATED position mately t-45 volts, forward-biasing diode CR301.
resistance is inserted between the cathodes. This The conduction of CR301 pulls the plates of V102
resistance acts as degenerative feedback and lowers (and therefore the grids of V103) to approximately
the gain of the stage, giving the desired control of the ~60 volts, cutting off V103. With V103 in a cutoff
deflection sensitivity. If the two halves of the tube Zondition, no signal from channel A appears in the
were identical and Rlll andR112 had exactly the same
value, then R123 would have no effect on the dc balance
of the differential amplifier. However, since these
components are not identical, BAL. control R104
adjusts the operating point of the differential amplifier
stages so that the two cathode voltages are equal and
no current flows through R123 to change the balance of
SIGNAL
the stage and move the vertical position of the trace. FROM -& V103A
A means of bringing the SENSITIVITY scales into V102A
calibration is provided by SENS. CAL. control R120.
This control acts as a voltage divider with R113 and
R114, changing the operating point of V102 toward
lower plate current, lowering the transconductance
R314~~~~8 R308
and the gain. In this manner the entire vertical am-
plifier may be brought into calibration.
OUTPUT
4-9. OUTPUT CATHODE FOLLOWER. The output
of differential amplifier V102 is connected through
coupling networks R121-L103 and R122-L104 to the
grids of output cathode follower V103. These net-
works are necessary to compensate for differences
in the frequency response of the two channels due to
switch and wiring capacitance. These networks are
VERT R3 8 I3 ITR-
not used in the channel B amplifier.
POS. ADJ. SO-S-1958
4-10. To achieve control over the vertical trace To -v
position, VERTICAL POSITION control R127-128 R317
varies the dc bias in the grid circuit of V103. This
in turn varies the cathode voltage of V103, and thus
the vertical position of the trace. Figure 4-4. Constant Current Generator
4- 2 01558-1 |
ACEC
HEWLETT-PACKARD
