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MODELS 610~, 6LOBR ELECTRO~BRS
CIRCDIT
DESCRIPTION
b.
Depressing
the ZERO CHECK Button,
SlO3,
connects
resistors
RLOL and Ill13
to output
ground.
This
effectively
removes
all
signal
from
the grid
of VLOL,
and the
input
impedance
is
reduced
to 10 megohms.
c.
An emitter
follower
stage,
transistors
QLOL and Q102, matches
the rela-
tively
high
impedance
output
of the
electrometer
tube
stage
to the
Low input
impedance
of the
differential
amplifier
stage
formed
by transistors
4103 and
9104.
This
latter
stage
drives
a second
differential
amplifier
stage,
tran-
sistors
QLOS and QlO6.
Resistors
R152 and RL53 prevent
Lock-up
of the amp-
lifier
under
overload
conditions.
d.
Transistor
Q106 drives
the grid
of the output
voltage
amplifier,
VL03.
Resistor
RL84 protects
V103 from drawing
excessive
grid
current;
capacitor
Cl13
is
a high-frequency
bypass.
e.
The zero
balance
controls
adjust
the
dc voltages
of the
electrometer
tube
screen
grids.
The screen
grids
of VlOL and VLOZ are returned,
in
effect,
to the
emitters
of transistors
Q103 and 4104 through
the
COARSE
and MEDIUM ZERO Switches,
SL04 and SLO5.
The emitter
voltage
of Q103 and
9104 can vary,
resulting
in a negative
feedback
loop
for
signals
in phase
at
the
electrometer
tubes
through
the 9103 and Q104 emitter
circuit
back
to the
VLOL and VlOZ screen
grids.
This
connection
stabilizes
the
electrometer
plate
potential
and tube
operating
points.
Also,
for
signals
arriving
at the VZOL
control
grid,
the
first
stage
gain
will
be much greater
than
spurious
signals.
f.
The voltage
drop
across
the l%.zLtiplier
Switch
resistors,
Rl56
through
RL66,
determines
the voltmeter
sensitivity.
A l.l-milliampere
current
through
the resistors
produces
a full-scale
meter
deflection.
On the higher
voltage
ranges,
resistors
R171 through
Rl73
are across
the
collectors
of Q103
and QL04 to reduce
the amplifier
gain.
This
assures
the amplifier
stability
when maxiawa
gain
is
unnecessary.
8.
The recorder
output
is
derived
from
the
current
flow
from VlO3 through
the ~Ltiplier
Switch
resistor,
With
the
Output
Switch,
S108,
on 3V, ?3 volts
for
full-scale
deflection
are
obtained
at
the output
connector,
3105,
by r1.L
milliamperes
flowing
through
resistor
R180.
With
S108 at 1 MA, resistors
R174
and R179 are connected
across
5105,
allowing
21 milliampere
*5% to pass
through
an external
Load.
h.
The second
triode
section
of V103,
connected
as a diode,
provides
warm-
up compensation
for
the
-265
volt
supply.
This
prevents
severe
out-of-balance
conditions
during
warm-up
and cool-down,
which
could
cause
excessive
eLectro-
meter
tube
grid
current
to flow
and result
in poor
drift
characteristics.
The "normal"
and "fast"
referred
to below
are only
the
positions
of the
FEEDBACK Switch.
"Normal
method"
is
when the
Switch
is
set
to NORMAL; "fast
method"
is when
the
Switch
is
set
to FAST.
1064R
23
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