Broadcast Electronics FM-5T, User Manual

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4-6
4-29. Five STATUS indicators illuminate to indicate an operational condition as follows: 1) the
FAILSAFE LED indicates the external interlock is closed, 2) the INTERLOCK LED indi
cates that the internal interlock loop is closed, 3) the BLOWER LED indicates that the air
pressure is correct for the PA stage to operate, 4) the FILAMENT LED indicates primary
ac power is applied to the filament transformer, and 5) the HIGH VOLTAGE LED indi
cates primary ac power is applied to the high voltage plate supply.
4-30.
METERING.
4-31. Seven front panel meters on the FM-5T and six on the FM-5TS are provided to indicate
transmitter operating parameters. Output power and output VSWR indications are pre
sented on a precision output power meter. Plate voltage and plate current information are
displayed on separate meters for optimum convenience.
4-32. Additional transmitter metering features include a six function multimeter. The multime
ter selects and displays information on vital transmitter operating parameters such as:
1) screen current, 2) screen voltage, 3) grid current, 4) grid voltage, 5) exciter forward pow
er, and 6) exciter reflected power. An iron-vane voltmeter is used to measure filament
voltage. A FILAMENT TIME meter is provided to indicate hours of filament circuit op
eration. On FM-5T models, primary ac voltage monitoring is provided by a primary ac
voltmeter. The meter selects and displays the voltage between all three phases of the ac
input. All meter currents are measured on the ground side of each supply to prevent high
voltages across the meters.
4-33.
EXCITER METERING.
The exciter operating parameters are displayed by two additional
meters and three status indicators. For detailed information on exciter metering, refer to
FX-250C exciter manual 597-1004.
4-34.
POWER SUPPLIES.
4-35. The FM-5T transmitter is designed for operation from a 196 to 252 volt three phase ac in
put. The plate supply is a conventional three phase power supply circuit. The remaining
FM-5T transmitter power supplies are single phase circuits which are obtained from two
phases of the three phase input. The FM-5TS transmitter is designed for operation from a
196 to 252 volt single phase ac input. All FM-5TS transmitter power supplies are single
phase circuits obtained from the transmitter ac input.
4-36. The grid bias and screen power supplies consist of conventional full-wave rectification and
choke input filter sections. A hum-null assembly consisting of a small unfiltered full-wave
rectified supply injects a 120 Hz pulsating dc voltage in series with the ground return of
the grid bias supply to cancel residual ripple from the screen supply in the tetrode amplifi
er.
4-37. The FM-5T plate supply is a three-phase primary, six-phase secondary supply. The pri
mary circuit is connected in a closed delta arrangement and the secondary is connected in
a wye configuration. The supply consists of a 3-phase full-wave bridge rectifier network
with an LC filter section. Advantages of this type of supply is good regulation and low rip
ple which requires little filtering. The FM-5TS plate supply consists of a single phase full-
wave rectifier network with a resonant LC filter stage. Power is applied to each plate sup
ply through a step-start circuit to reduce the inrush current at power-on. This limits
stress and extends component life.
4-38. The filament supply consists of a variable transformer assembly which is used to adjust a
high-current low-voltage regulator assembly. The regulator assembly is designed to regu
late a wide range of ac input potentials into a stable 240
±
1% volt output.
4-39. Each modular component of the transmitter is equipped with a self-contained ac power
supply. In addition, a battery back-up supply in the transmitter controller maintains op
erational information during power outages.