ON
3
CIRCUIT
DESCRIPTION
AMPLIFIERS
The Type CA Plug-In
Unit
consists
of two
identical amplifier channels
and a channel
switching
multivibrator. The
following descrip
tion of the amplifiers applies equally well to
either channel.
Input
Coupling
and
Attenuation
The signal to be displayed
is applied to the
input
cathode
follower V3323
(V4323) by way
of the
AC-DC switch
and the VOLTS/CM switch.
The
AC-DC switch is a two-position slide
switch
that
bypasses C3300
(C4300) in the
DC position
so the input is
de coupled. In
the AC
position of
this switch the signal
must
pass
through C3300 (C4300) so the dc com
ponent
of the signal
is blocked.
The
VOLTS/CM switch is a 9-position rotary
switch
that selects the various frequency-
compensated
rc attenuator sections. The
sen
sitivity
of the
unit is
.05
volts/cm, The
input
voltage
is reduced by the eight individually
selected attenuator sections to give nine fixed
calibrated
ranges.
Input
Stage
The
input
stage
consists of the cathode follower
V3323
(V4323)
and the cathode-coupled phase
inverters
V3334
and V3354 (V4334 and V4354).
The
control-grid
d
c
level of V3334 (V4334)
is established
by
the d
c connection to the cathode
of
V3323
(V4323). The control-grid dc level
of V3354
(V4354) is
adjustable by
means of the
DC
BAL controls so that the dc level of the
cathodes of V3334
and
V3354 (V4334
and V4354)
can
be made
equal. Any dc level difference
between
these two cathodes would act
as a signal
and
cause the trace to
shift
position when
the
VARIABLE
control is rotated. The
VARIABLE
gain
control establishes the amount
of
cathode
coupling
and thus allows the stage gain to be
varied over about a 2 1/2 to 1 range.
The
GAIN
ADJ control permits the basic
gain
of the
unit to be accurately set to agree
with
the
front-panel
calibration.
Polarity and
Positioning
With the
POLARITY
switch in the NORMAL
position the displayed waveform will have the
same
polarity
as the input signal.
Placing
the
POLARITY switch
in the INVERTED
position
reverses
the
signal-grid
connection
of
V3364
and V3374 (V4364
and
V4374) and
inverts the
displayed
waveform. Rotation of the
VERTICAL
POSITION control forces one
plate
of
the
input
stage
toward a
higher potential and the
opposite
plate toward a
lower
potential. The
resulting
de level
shift moves the trace vertically.
Amplifier Stage
and Output
CF
The signal is further amplified
by
V3364
and V3374 or V4364 and V4374,
depending
on
which
channel is conducting. V3364 and
V4364
have
a common
plate load and likewise V3374
and
V4374.
Since one amplifier is always cut
off while the other
is conducting,
the
shunt
loading effect
is negligible.
V4383 is the output
cathode
follower
that
provides a low-impedance source
for
driving
the
oscilloscope's vertical amplifier.
The
Vert.
Pos.
Range
control located in the
grid
circuit
of the output cathode followers permits the trace
to
be centered vertically under no-signal
con
ditions.
SWITCHING
CIRCUIT
A ONLY
, B
ONLY
V3375
is
a multivibrator
that is
controlled
AA
Circuit Description - Type
CA
3-1