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CIRCUIT
DESCRIPTION
MODELS 6LOB, 6LOBR ELECTROMETERS
b.
When thereis
no input
signal
and the
zero
is
set,
the
current
(i,)
in the
upper
Loop of Figure
14 equals
that
in
the
lower
Loop (ib):
La = ib.
With
an
input
signal,
the
circuit
reacts
as follows:
1.
When a positive
voltage,
cei,
is
applied
to the
input,
the amplifier
drives
the V103 grid
less
negative,
and the plate
current,
i,,
is
increased.
Increasing
ia causes
a voltage
drop
through
the E6rLtipLier
Switch
resistor,
Rm.
At equilibrium
this
drop
equals
ei,
and therefore,
it
keeps
the
voltage
drop,
ea, across
the
amplifier
to a fraction
of the
input
voltage.
2.
when a negative
voltage,
-ei,
is
applied
to the
input,
the
amplifier
drives
the VL03 grid
more negative
with
respect
to the
cathode,
and ia
is
decreased.
The current
in
the
Lower
Loop,
Fb, becomes
greater
than
i,,
producing
a VOLtage
drop,
eo, across
R,,,.
The drop
is
sufficient
to null
the
negative
input
voltage,
ei,
again
keeping
the
voltage
drop
across
the
ampli-
fier
to a fraction
of
the
input
voltage.
3.
The voltage
drop
across
the
amplifier
is
ea
=
=i
kc1
where
k is
the
Loop gain,
approximately
LO5 on the 0.001
to 0.3-volt
ranges.
c.
The output
stage,
V103,
drives
the amplifier
ground
at the
same poten-
tial
as the
input
signal.
This
means the ground
terminal
of
the
amplifier
is
not
at
chassis
ground,
but
is
connected
directly
to the
cathode
of V103.
Ikillg
this
circuit,
the
input
can accept
voltages
up to rlO0
volts
without
input
dividers.
This
maintains
high
input
impedance
and eliminates
instabilities
which
can occur
with
high
resistance
dividers.
NOTE
On the
schematic
diagram,
amplifier
ground
is
called
"floating
ground"
and the
output
amplifier
ground,
"output
ground."
d.
All
power
supplies
are
floating
with
respect
to the
input
or chassis
ground.
The +250 and -265
volt
supplies
are provided
for
the
output
voltage
amplifier,
V103.
Separate
regulated
-10 and +21 volt
supplies
provide
power
for
the amplifier
and are.referred
to floating
ground.
NOTE
Refer
to Schematic
Diagram
17795E for
circuit
designations.
3-3.
VOLTMETER CIRCDIT.
a.
Two balanced
5886 electrometer
tubes
are
at the voltmeter
amplifier
input.
Their
filaments
are
operated
in parallel
from
the
regulated
~21 volt
supply
through
dropping
resistors,
R119 and R122.
Resistors
RlOL and R113 protect
the
control
grid
of VlOl,
the
active
electrometer
tube,
from
excessive
grid
currents
due to overloads.
Capacitors
Cl01
and Cl10
are high-frequency
bypasses.
The
control
grid
of VL02 is
returned
to floating
ground,
22
1064R
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