HP 3400A - Appendix A Manual Changes; Section VII, Table 7-3 Changes; Change #2 (Serial No. 2225 A30740 and BELOW); Section IV Changes (4-16 thru 4-18)

Appendix
A
Model
3400A
Section
Vil,
Table
7-3
Changes.
Do
the
following
changes
in
the
table.
Reference
Designator | -
Description
Change to 1 K 1% .125W Resistor
0757-0280
R622
0698-3454
Change
to
4.22
K
1%
.125W
Resistor
R625
0683-7545
Change
to
750
K
5%
.25W
Resistor
R629
2100-3355
Delete
100K
Potentimoter
CHANGE
#2
(SERIAL
No.
2225A30740
and
BELOW)
The
instruments.
with
serial
number
2225430740
and
below
had
different
A2
and
A7
Assemblies
installed.
Because
the
rear
panel
was
also
different,
the
instruments
cannot
be
retrofitted
for
the
new
assemblies
presently
listed
in
Table
7-3.
If
any
A2
or
A7
Assembly
needs
replacement,
use
the
old
part
number
listed
in
Table
A-2.
Section
IV
Changes.
Change
paragraphs
4-16
thru
4-18
to
the
following
(use
Figure
A-3
with
the
paragraphs):
4-16.
The
impedance
converter
assembly
utilizes
a
nuvistor
cathode
follower
circuit
to
match
the
high
output
impedance
of
the
input
attenuator
to
the
low
input
impedance
fo
the
second
attenuator.
The
cathode
follower
circuit
preserves
the
phase
relationship
of
the
input
and
output
signals
while
maintaining
unity
gain.
4-17.
The
signal
input
to
the
impedance
converter
is
RC
coupled
to
the
grid
of
cathode
follower
V201
through
C201
and
R203.
The
output
signal
is
developed
by
Q201
which
acts
like
a
variable
resistance
in
the
V201
cathode
circuit.
The
bootstrap
feedback
from
the
cathode
of
V201
to
R203
increases
the
effective
resistance
of
R203
to
the
input
signal.
This
prevents
R203
from
loading
the
input
signal
and
preserves
the
high
input
impedance
of
the
3400A.
The
gain
compensating
feedback
from
the
plate
of
V201
to
the
base
of
Q201
compensates
for
any
varying
gain
in
V201
due
to
age
or
replacement.
4-18.
Breakdown
diode
CR201
controls
the
grid
bias
voltage
on
V201
thereby
establishing
the
operating
point
of
this
stage.
CR202
and
R211,
which
are
across
the
base-emitter
junc-
tion
of
Q201,
protects
the
transistor
from
+75
V
power
supply
failures.
Regulated
de
is
supplied
to
the
V201
filaments
to
avoid
inducing
ac
hum
in
the
signal
path.
This
also
prevents
the
gain
of
V201
from
changing
with
line
voltage
variations.
Section
!V
Changes.
Add
paragraphs
4-45/4-46
to
the
section
(use
Figures
A-4
and
A-5
with
the
paragraphs).
4-45. -6.3 Volt Supply
4-46.
The
regulated
-6.3 volt
supply
consists
of
a
full-wave
rectifier
(CR716
and
CR717)
whose
output
is
filtered
by
C2
and
regulated
by
Q3.
Emitter
follower
Q705
is
connected
to
the
-17.5
volt
supply
which
provides
a
reference
for
the
-6.3
volt
supply.
Series
regulator
Q3
acts
as
a
dynamic
variable
resistor
in
series
with
the
output
to
oppose
changes
in
the
output
voltage.
Section
VI,
Figure
6-1
Changes.
Use
component
locator
and
schematic
in
Figure
A-3.
Section
V!,
Figure
6-4
Changes.
Use
component
locator
in
Figure
A-4
and
schematic
in
Figure
A-5.
The
shaded
area
on
the
schematic
pertains
to
the
changes.