I could be wrong but the clarity of the Plexiglas is not a parameter of interest in amplifier performance...

the question is, is the fog a film from an internal component failing (sounds bizarre) but if the amp works fine go get another piece of plexi and slide it in

the US Amps tube amps got plenty hot and could affect the shape of the plexiglas

 

I have a us amps TU4360 mounted under a seat and the plexi is just like new. Don't think heat is the issue unless there is a failing component. But hard to believe that something would get hot enough to distort plexi and not fail completely. I have seen capacitors release a gas so to speakbut that was only after catastrophically failing. If the amp still works then.......

 

Sorry people I had surgery this morning, and like I said, its MINTY

 

looks like dust that stuck to some condensation. take the panel off and clean it.

 

Agreed, but I have never seen that before and I have 3 US Amps amplifiers... Strange

 

I'll take it apart in a bit. I've personally owned 3 of these and seen many more, this is new to me too

 

Its because of component failure