Power Control Circuit; Maintenance; Disassembly; Access To Power Amplifier (Rear View) - GE Mastr II Maintenance Manual

LBI-4732
POWER AMPLIFIER
POWER CONTROL CIRCUIT
When the transmitter is keyed, recti-
fied RF from CR201 is applied to the base
of switch Q204, turning it on. Turning on
Q204 turns on voltage regulator Q206 which
supplies a constant voltage to Power Adjust
potentiometer R216.
Q208, Q209 and Q210 operate as an am-
plifier chain to supply voltage to the col-
lector of Q201 (Ampl-1). The setting of
R216 determines the voltage applied to the
base of Q208. The higher the voltage at
the base of Q208, the harder the amplifiers
conduct, supplying more collector voltage
to Q201. The lower the voltage at the base
of Q208, the less collector voltage is sup-
plied to Q201. Reducing the supply voltage
to Q201 reduces the drive to Q202 and Q203,
thereby reducing the power output of the PA.
The power output can be adjusted by R216
from approximately 15 to 50 Watts.
Temperature protection is provided by
Q205, Q207 and thermistor RT201 which is
mounted in the PA heatsink. Under normal
operating conditions, the circuit is inact-
ive (Q205 is on and Q207 is off). When the
heatsink temperature reaches approximately
100°C, the resistance of RT201 decreases.
This increases the base voltage applied to
Q205, turning it off. Turning off Q205
allows Q207 to turn on, decreasing the volt-
age at Power Adjust potentiometer R216.
This reduces the base voltage to Q208 which
causes Q209 and Q210 to conduct less, re-
ducing the collector voltage to Q201
(Ampl-1). This reduces the transmitter
output power, keeping the heatsink at a
maximum of approximately 100°C. When the
heatsink temperature decreases below 100°C,
the temperature control circuit turns off,
allowing the normal transmitter power out-
put.
MAINTENANCE
DISASSEMBLY
For a more complete mechanical parts break-
down refer to the station manual. To service
the transmitter exciter from the front:
1.
2.
3.
Turn the two latching knobs ~ coun-
terclockwise to unlatch the Radio
Panel Front Door. Refer to Figure 5.
Swing the Radio Panel Front Door down
as shown.
Remove covers.
To service the transmitter Power Amplifier
from the rear:
1. Remove the top two screws
{8)
on the
Intermittent or Continuous'nGty Power
Amplifier. Refer to Figure 6.
6
2.
Figure 5 - Access To Exciter - Front View
Figure 6 - Access To Power Amplifier -
Rear View
Swing the Power Amplifier down as
shown. Remove the top cover of the
Power Amplifier.
NOTE
If the heatsink blower option is
present, this blower must be re-
moved before the Power Amplifier
can be lowered.
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