Twice within the past six months we have had amplifiers fail due to the loss of
all of the power supply filter capacitors in one "bank" of the supply. Both
amplifiers (an Alpha 76 and a SB-220) were being run on 240 V AC. In both
cases the filter capacitors were "relatively" new. In one instance the failure
occurred when the amp was in "standby" mode during a break in a contest and in
the other the unit seemed to have failed AFTER it had been turned off and
prior to the next use. At the time both cases were ascribed to "random"
failures, unknown cause, and possibly a "weak" sister in the capacitor bank.
However, a recent comment by an experienced HV power supply builder, has
brought up the subject of a possible "wild leg" in the 240 V AC line to which
the amps were attached. According to this suggestion, a large transient
VOLTAGE swing on one leg of the 240 V mains put an over-voltage on the
capacitor string causing them to fail. Both units were protected from CURRENT
surges and no evidence of excessive current flow could be found. This was
said to be a known fault either with residential power line transformers or
with improperly balanced house wiring.
My first reaction was to take all this with a "large grain of salt" but then
there is always a chance that such a phenomena can occur. If anyone has had
any similar experience or know of a rational explanation, I'd really like to
know about it.
Thanks,
Joe, W5ASP
--- Joseph Staples
--- w5asp@earthlink.net
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