Load Fault Indicator
The "LOAD FAULT" LED indicator will light and the amplifier will be bypassed if the
band switch is set on the wrong frequency range, if the load SWR is excessive, or if the
output power level is excessive.
To reset a "LOAD FAULT" indication:
1. Determine and correct the cause of the problem.
2. Place the amplifier "STANDBY-OPERATE" switch to "STANDBY" and then
back to "OPERATE".
Note: When the ARI-500 is used, the STANDBY-OPERATE switch is under control of
the ARI-500. The amplifier will automatically be put in OPERATE when the
transceiver is keyed, regardless of the STANDBY-OPERATE switch position on
the ALS-600. When a fault occurs, the ARI-500 can be configured to
automatically re-set the ALS-600 after approximately 5-seconds. If the ARI-500
is not configured for automatic amplifier fault re-set, you must cycle the amplifier
power switch OFF and then ON to re-set the fault circuitry.
Note: When the ALS-500RC Remote Control Head is used (with or without the ARI-
500), the STANDBY-OPERATE function is controlled by the POWER OFF-ON
switch on the ALS-500RC.
The load fault detector circuit is located on the output filter board and measures the
reflected power presented by the output filter network and the SWR directional coupler.
The sensitivity of the circuit is adjusted by R304 and R601. C324 is a factory adjustment
that controls the impedance of the detector circuit. This capacitor is adjusted for
minimum detector voltage on 7 MHz with a 50 ohm load. Do not adjust any components
in this circuit without consulting the factory.
SWR Considerations
A high SWR (Standing Wave Ratio) causes higher voltages and/or currents to appear at
the output connector of the amplifier. This problem occurs with all amplifiers regardless
of whether tubes or semiconductors are used in the output stage.
Vacuum tube amplifiers have the reputation of handling a high SWR quite well. This
reputation probably exists for two reasons: First, most vacuum tube amplifiers use
adjustable output networks. Second, nearly all vacuum tubes handle momentary
overloads extremely well.
In tube amplifiers with tunable Pi or Pi-L networks, the only components affected by a
high load SWR are those between the loading adjustment capacitor and the output
connector. When the output network is properly adjusted, the SWR cannot affect tube
life.
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