Alpha 8100 Operating Manual page 34


One of four situations will typically result in a fault:
• Incorrect gain. Output too low or too high for the input power supplied.
• High reflected power (SWR).
• Incorrect plate voltage (too high).
• RF arc in output circuit including antenna.
If the 8100 encounters unsafe operating conditions, it enters a protective "Fault" mode. When this
happens, the tubes are biased off and the relays are placed in the bypass mode, so that RF from
the radio goes directly to the antenna. The FAULT LED on the front panel will flash on and off for a
period of about 4 seconds, after which the amplifier will attempt to go back into OPERATE mode,
unless the OPER/STBY switch has been placed in the STBY position. This 4 second period can be
shortened by toggling the OPER/STBY switch.
While the FAULT LED is flashing, the Ip and HV LEDs are used to indicate which of the four fault
conditions caused the amplifier to enter fault mode.
Fault type 1
Neither Ip nor HV LEDs are lit. Output relay did not close. This fault will rarely be encountered, but
if it is, it must be investigated further immediately, as continued operation with this fault could
cause additional damage to the amplifier.
Fault type 2
Ip LED is blinking. This indicates that the plate current in the tubes exceeded 1.5 amps. This could
be caused by the amplifier being mistuned or by overdriving the amplifier. If neither of the above
is the case, then a problem in the bias control circuitry may be indicated.
Fault type 3
Both Ip and HV LEDs are blinking. This indicates that the gain of the amplifier has fallen below 10
dB. This is an important safety feature of the amplifier, as many different problems in the amplifier
or with its operation can be detected as a drop in gain. To avoid this fault occurring while the
amplifier is being tuned up, the gain fault detection is disabled when drive power to the amplifier
is below approximately 20 watts. This allows correct initial amplifier tuning to be achieved before
going to full power.
Fault type 4
HV LED is blinking. This indicates a reflected power fault. The 8100 is set up to trip when the
reflected power exceeds approximately 250 watts. At 1,500 watts output, this would represent an
SWR of approximately 2.4:1. Possible causes for this fault are in the antenna. No antenna could be
ALPHA 8100 OPERATING MANUAL
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