4-8
4-50.
Minimal filtering is required as only 4.2 percent ripple is output from the rectifiers. One
requirement of the multiphase supply, however is that the primary ac input must be bal
anced to within the percentage of ripple voltage which is to be obtained from the supply.
Constant primary ac line unbalance can be corrected by the use of primary taps or a
tapped three-phase autotransformer.
4-51.
Filtering for the supply is accomplished by a one-section choke-input filter. The choke is
inserted in the negative leg of the rectified output to eliminate the dc potential between the
choke and ground. The negative leg of the supply is referenced to ground through the PA
stage current meter shunt. A single shunt capacitor bypasses residual ac ripple at fre
quencies of 300 to 360 Hz and higher to ground. A bleeder resistor connected across the
supply increases regulation and, in conjunction with high voltage discharge solenoid K5,
enhances safety. A series resistance in the anode dc feedline limits peak energy in case of
arc-overs in the power amplifier stage or high voltage discharge solenoid operations.
4-52.
Component stress at power-on is eliminated by a step/start circuit which limits plate sup
ply inrush current. The step/start circuit is interlocked through contacts of the filament
circuit breaker and the filament/driver contactor to assure that the filament circuit is ener
gized before a high-voltage-on sequence can be initiated. The controller will energize the
step contactor via K6. After 100 milliseconds, the controller will energize the start contac
tor via K5. The step contactor will deenergize after it has been energized for 160 millisec
onds. In this manner, the current limiting resistors will only be subject to heating during a
100 millisecond interval between the step/start relay closures.
4-53.
PA SCREEN GRID POWER SUPPLY.
The screen power supply is a full-wave bridge-recti
fied supply with a single L-section filter. The primary of the screen transformer is con
nected through CB3 to the step/start contactors. The output of the screen supply is adjust
able with a variable autotransformer connected in the primary of the screen transformer.
A dc motor connected to the variable autotransformer allows both manual and automatic
control of the screen voltage. The choke in this supply is connected in the negative leg of
the supply to eliminate the dc potential between the choke and ground. A bleeder resistor
connected across this supply improves regulation and enhances safety by discharging C6.
4-54.
PA CONTROL GRID POWER SUPPLY.
The control grid bias supply is a full-wave bridge-
rectified supply with a single L-section filter. The primary of the supply is connected to
the primary ac input through CB5 and filament/driver contactor K3. A bleeder resistor
connected across this supply improves regulation and enhances safety by discharging C9, a
relatively high capacity electrolytic capacitor.
4-55.
Hum Null Supply.
The ground path for the grid bias supply is
routed through the hum-
null circuit which introduces a small 120 Hz pulsating dc component into the control grid
bias supply to cancel hum in the PA tube from the screen supply. The amount of voltage
added to the negative side of the control grid bias supply is adjusted by R10. This voltage
is out-of-phase with the 120 Hz ripple component of the screen supply.
4-56.
PA FILAMENT SUPPLY.
The PA filament supply is a low-voltage high current ac supply.
Overload protection for the circuit is provided by circuit breaker CB5. Filament voltage
regulator VR200 provides a stable ac input voltage environment. Variable transformer T5
provides accurate filament voltage adjustment. A
FILAMENT TIME
meter indicates
hours of filament circuit operation.
Summary of Contents for FM-5T
Page 1: ...FM 5T FM 5TS 5 KILOWATT FM BROADCAST TRANSMITTERS July 1999 IM No 597 0033 014 ...
Page 14: ...1 3 FIGURE 1 1 FM 5T FM 5TS TRANSMITTER 597 0033 1 COPYRIGHT 1990 BROADCAST ELECTRONICS INC ...
Page 29: ...2 13 COPYRIGHT 1997 BROADCAST ELECTRONICS INC 597 0033 415 FIGURE 2 4 TRANSFORMER TAPS ...
Page 32: ...2 16 597 0033 406 FIGURE 2 6 FM 5T PRIMARY AC WIRING COPYRIGHT 1997 BROADCAST ELECTRONICS INC ...
Page 46: ...3 9 TABLE 3 2 INDICATOR CHECKLIST 597 0098 412 ...
Page 61: ...4 19 FIGURE 4 5 PA CAVITY 597 0032 32 COPYRIGHT 1997 BROADCAST ELECTRONICS INC ...
Page 83: ...5 22 WARNING DISCONNECT POWER PRIOR TO SERVICING BLANK PAGE ...
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