[CQ-Contest] OT Amplifier question

[Charles Morrison]

Im asking because of the great wealth of knowledge, forgive the off topic
post, but here goes.

I have an 80M dipole cut for the bottom of the band.  As I gradually move up
the band, SWR slowly increases from a 1:1 match at 3.55mhz to over 3:1 at
3.9mhz.  For convenience sake, I've installed a Heathkit SA-2006A inline to
allow easy access for occasional SSB operation.  Once adjusted, the SWR
readings behind the tuner are a nice 1:1 match again.   I know that a tuner
is not the way to go, but it was a convenience thing.

Question is this.  Why at true reasonance at the bottom of the band, I can
tune my Alpha 99 to legal limit with approx 75w drive, however when the
tuner is switched from bypass to inline, and I change frequency to the upper
portions of 75m and adjust the tuner for a similar 1:1 swr, the amplifier
trips?  To head off quick answers, yes, I've readjusted the amplifer for a
different portion of the band, starting with the suggested settings and
tuning and peaking.  However, if drive beyond about 45w is applied, either
the amplifier will arc or it will trip.

Thanks
Charlie
KI5XP