KC-300 amplifier sound gets quiet after a while

[dojec]

I noticed if I'm playing with my KC-300 amplifier, after a while it only plays very silently.
I had this issue on different keyboards, so I suppose the issue is in the amplifier itself.

If I let it cool off, I get full power again.
Somebody had the same experience?
Is it worth to be fixed or better to go find another amplifier?