[Antennas] Question on Balun and use of one and type???

[Steve Jones]

I have an antenna called a German Quad which is supposed to be or have four
sides but due to my landscape layout, I could only come up with three
supports. The antenna is 236' in length, put up horizontally to the ground
and 40' up in the air on all three coiners. It is feed in one corner with a
matching stub of 28' of 450 ohm ladder line that drops vertically down from
one of the three coiners and then to coax and in to my shack where I use a
Drake MN2700 tuner to tune for use on other bands such as 10-20 meters. It
is almost flat across the entire 40 meter band and about 200 khertz on 75/80
meter band. Well this antenna has worked great until about a year ago I
noticed my SWR was going through the ceiling and the tuner was getting very
warm. I decided to replace the 9913 as this was the only thing that I could
determine was causing the problem. When I cut the run at the connection of
the 450 ladder line and coax, water ran out of the 9913 like a river.
Problem solved I thought. I had about a 100' run from my shack to the coax
joining the ladder line. Well the only thing I changed was the type of coax
which is now LMR400 because I had a 60' section laying around, and the
length which went from about 100' down to 60'. Now I get RF in my shack like
crazy, I can't even tune the bands 10-20 and run any power without so much
RF, I can't even operate and enjoy it, and here lately, I have noticed my
SWR curves have changed somewhat from a tuning chart I did and the tuner is
getting hot again, especially on 75/80 meters.

Does anyone of any thoughts on how I could correct this and get this great
antenna working like it use to on 10-75/80 meters. I never used a balun
before and then antenna worked great and again the only thing that has
changed is the length and the type coax I am using and it is hard to believe
water has gotten in to the LMR400. I would appreciate any and all feedback
that is positive and helpful, no insults or negativism needed here. Thank
you in advance for your help and 73, Steve