If the filter has 100W in and only 80 watts out then it is acting as a good
swamping resistor.
These were common a few years ago with AB1 amps. The problem is that the
filter is probably getting hot
and this could affect performance and in the end burn up the filter. This
was the case with a popular
pre-amp made for insertion between transceiver and antenna. One Low pass
filter had a large insertion loss
plus they scrimped on the insulation (they used very thin plastic
insulation). After about one years use in active stations
(such as mine) the filter failed and nearly cost me my amp or at least the
tubes in my amp...and this was an old NCL-2000
with 800W out. They had to replace nearly 300.
Be careful. And manufacturers spell out your insertion loss both in db and
power (say per 100W out)!
73 Dave K4JRB
.
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