I have 4 cats myself and a Class A amp so I know the problem. Real easy. Put something on top of the amp when its not in use. Artificial plants or some decorations should do. Something that easy to take off when the amps in use. Just put it back on when your finished listening.
Cats always look before they jump on top of something. If there's something in the way and no where to land they won't try to jump on it.
Cats always look before they jump on top of something. If there's something in the way and no where to land they won't try to jump on it.