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R-9320
R-9450
POWER
TRANSFORMER
The
transformer
consists
of
three
windings:
primary,
filament
and high voltage.
During
a cook
cycle,
the 240 volts
A.C. applied
to the
primary
winding
of the transformer
through the cook relay
contacts
is converted
to 3.45 volts AC.
on
the
filament
winding
and approximately
2350 volts
A.C. on the high
voltage
winding.
The 3.45
volts
A.C. voltage
heats the
magnetron
filament.
This
causes the
tube
cathode
to
readily
emit
the electrons
necessary for tube conduction
whenever
the
negative
4000 D.C. voltage is applied
to the
cathode.
The 2350 volts A.C. voltage
is
fed to the
voltage doubler
circuit.
VOLTAGE
DOUBLER
CIRCUIT
The
voltage
doubler
circuit
consists
of a rectifier
and
a capacitor.
The 2350 volts
A.C. from
the high voltage
winding
of the power transformer
is applied to
the
voltage
doubler
circuit,
where
it
is
rectified
and converted
to
approximately
4000 volts negative
D.C. needed
for
magne-
tron operation.
Rectifier:
The rectifier
is solid state device that
allows
current
flow in one direction,
but prevents current
flow in
the
opposite
direction.
This
acts as rectifier
changing
alternating
current
into pulsating D.C.
WITHOUT
MAGNETIC
FIELD
;
7 CATHODE
Figure 6. Basic Magnetron without
Magnetic Field
High
voltage
capacitor:
The capacitor
is able to
store
energy on one half of the power cycle and release it along
with
the
transformer
output
to
produce
approx.
4ooO
negative D.C. volts to the magnetron.
MAGNETRON
TUBE
The basic magnetron
tube is a cylindrical
cathode within
a
cylindrical
anode surrounded
by a magnetic field. When the
cathode
is heated
by the filament
winding
of the power
transformer,
electrons
are given off by the cathode.
These
negatively
charged
electrons
are attracted
to the
more
positive
anode of the tube when the negative 4000
D.C.
voltage is applied to the cathode.
Ordinarily,
the electrons would travel in a straight line from
the cathode
to the
anode as shown in Figure 6. But the
addition
of
a magnetic
field,
provided
by
permanent
magnets surrounding
the anode, causes the electrons to take
an orbital
path between the cathode and anode,
Figure 7.
As
the electrons
approach
the anode, they travel past the
small resonant
cavities that are part of the anode. Interac-
tion
occurs, causing the resonant cavities to oscillate at the
very high frequency
of 2450 megahertz.
This
RF
energy is
radiated
from
the magnetron
antenna
into the waveguide
into
the
cooking
cavity
feedbox,
and finally
into
the
cooking
cavity
where food has been placed to be cooked.
WITH
MAGNETIC
f-7
-
FIELD
I-'
1 1 i 47
n
,n
ANODE /
i CATHODE
COOKING LOAD'
Figure 7. Basic Magnetron with Magnetic Field
27
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