Heathkit HP-23A - Chassis Photograph

Page 17
CIRCUIT
DESCRIPTION
To
better
understand
the
circuit
operation,
refer
to
the
Schematic
Diagram
while
reading
the
following
description,
Each
section
of
the
Power
Supply
will
be
discussed
individually,
PRIMARY CIRCUIT
The
AC
OFF
switch,
circuit
breaker,
trans-
former
primary,
and two
terminals
of
the
power
output
Socket
are
wired
in
series
across
the
AC
line,
The
Power
Supply
may
be
controlled
by
its
AC
OFF
switch,
or
by
the
off-on
switch
in
the
equipment
being
used
with
it,
The
dual
pri-
mary
winding
may
be
connected
in
series
for
240
VAC
line
operation,
or
inparallel
for
use
on
a
120
VAC
line,
HIGH VOLTAGE SECONDARY CIRCUIT
The
high
voltage
winding
applies
approximately
282
volts
AC
(RMS)
to
a
full-wave
voltage
doub-
ler
rectifying
circuit
consisting
of
silicon
diodes
Di,
D2,
D3
and
D4,
and
capacitors
C1
and
C2,
These
diodes
are
connected
so
that
during
one-
half
cycle,
capacitor
C2
becomes
charged;
and
during
the
next
half
cycle
capacitor
C1
is
charged,
Resistors
R1, R2,
R3,
and
R4
are
connected
in
the
circuit
to
provide
a
discharge
path
for
capacitors
C1
and
C2,
The
capacitors
are
charged
individu-
ally,
but
discharge
in
series
to
produce
aDC
volt-
age
equal
to
approximately
twice
the
applied
peak
AC
voltage,
Excellent
dynamic
regulation
is
pro-
vided
by
the
large
capacitance
values
of
C1
and
C2,
The
output
of
the
voltage
doubler
circuit
has
a
low
ripple
content
and
no
further
filtering
is
re-
quired,
LOW VOLTAGE CIRCUIT
‘The
low
voltage
winding
is
tapped
so
that
either
95
or
125
volts
AC
(RMS)
may
be
applied
to
a
half-wave
voltage-doubler
rectifying
circuit
consisting
of
diodes
D5
and
D6,
and
capacitors
C3
and
C4,
Capacitor
C4
is
‘also
used
with
choke
L1
and
capacitor
C5
in
a
pi
filter,
C4
being
the
input
capacitor
in
the
filter
network,
The
use
of
a
high-capacitance
input
pi
filter
network
provides
a
well
filtered
DC
output
that
has
a
very
low
percentage
of
ripple,
BIAS VOLTAGE CIRCUIT
The
bias
voltage
is
obtained
from
the
lowtap
on
the
low
voltage
winding,
About
95
volts
AC
(RMS)
is
applied
to
half-wave
rectifier
diode
D7,
Capacitors
C6
and
C7,
with
resistor
RT,
pro-
vide
a
filter
network
to
remove
the
ripple
from
the
bias
voltage,
Either
-130
volts
of
fixed
bias
or
from
~40
to
-80
volts
of
adjustable
bias
may
be
used
by
connecting
to
the
appropriate
pin
of
the
power
output
socket,
The
adjustable
bias
is
set
by
the
Bias
Adjust
control
R9,
Resistors
R8
and
R10
are
used
to
limit
the
range
of
the
Bias
Adjust
control,
FILAMENT VOLTAGE CIRCUIT
The
12,6
volt
filament
winding
is
center
tapped
so
that
either
6,3
or
12,6
volts
AC
can
be
ob-
tained,