[TowerTalk] SWR Problem with Tri-Bander - help!

[RLVZ@aol.com]

Hi Guys,

I've got a Hy-Gain TH3-Mark4 that has a rather unusual SWR problem and wonder 
if you have any thoughts on fixing the problem.  Here's the scoop:

1) The SWR is always fine on 10 and 20 meters.
2) On 15-meters the SWR starts out fine but the longer I transmit the higher 
it goes.  Such as, when running 500 watts the beginning SWR is 1.3 to 1 but 
after 45 minutes it's 2 to 1. 

Here's various things I've tried but they didn't fix the problem:
1) Replaced the coax.
2) Replaced the balun.
3) Replaced the 15-meter traps on the driven element.
4) Took all traps apart and checked for solid connections. 
5) Locked the elements together with aluminum screws.

This is not my main antenna so it's not a life or death matter.  But I really 
like the antenna and want to correct the problem so I have a working backup 
and multiplier antenna.

Any idears?

Thanks!   Dick- K9OM