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The final amplifier employs a pair of 4CX10,000D power tetrodes,
in a push-pull grounded cathode type circuit.
These tubes are
conservatively rated at the 20KW output level.
The plate circuit
consisted of a distributed shorted 1/4 wavelength line.
This
line is tuned by pivoting a shorting bar at one end to chango
the electrical length of the line.
The output circuit consists of an inductively coupled balun
which is rigidly mounted in the amplifier enclosure and is at
d.c.
ground at all points.
The output loading is adjusted by
means of a vacuum capacitor
a
cross the output balan.
The tube socket is of a special design for VHF frequencies.
The
RF by-passing for filaments and screens is built into the socket.
At the output of the amplifier there is the micro-match unit,
which is used to meter the r.f.
power of the transmitter and to
indicate the standing wave ratio of the transmission line.
This output is connected directly to a low pass filter that sub-
stantially eliminates the second and higher order harmonics.
The
filter is 6-1/8" transmission line with distributed filtering
elements inside.
The output of the filter is fitted for a 3-1/8"
E.I.A.
flange.
The filter is supplied as part of the transmitter
and is tuned to the customers frequency at the factory.
All power supplies in the FM-2013use silicon rectifiers.
All vol-
tage supplies in the Amplifier are separate and adjusted and op-
erated independently for optimum amplifier operation.
All power supplies are protected by primary circuit breakers or
fuses and the
secondary of each power supply is protected by d.c.
relays in the secondary return.
The high voltage plate supply is a
3
phase,
full wave bridge con-
figuration with a choke input.
This supply is rated at 6500 V.
d.c.
at 5 amps.
For preliminary testing this supply can be
switched.to about 3200 volts.
The screen and
grid
bias supplies for the Amplifier are single
phase full- wave brp se configurations.
The screen supply is
rated at 1500 volts at 500 ma.
Both of these supplies can be
adjusted from the front panel of the power cabinet.
The driver plate supply is a single phase full-wave type of de-
sign with a double section choke input type of filtering.
This supply is variable by means of a motor driven variable pri-
mary transformer and is controlled from the front panel of the
P.1i. power cabinet.
This supply is capable of about 3000 volts
at 500 ma.
The 20K'd Power Amplifier and t.ie Intermediate Power
Amplifier are totally enclosed, both tubes and components,
in
a non-ferrous type housing.
Air from individual blowers cool
both tubes and parts.
6/22/61
-2-
FM- 20B
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