Schematic for Melos hc 180

I have a Melos hc 180 that breaks up at about 40 watts. Prior to that it seems to do fine. I have checked the tubes and they test ok. If anyone has papers on this amp or has suggestions please let me know. Thanks. Tom
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How do you know that it is breaking up at 40 watts? Are your speakers 4 or 8 ohm? What is the make and model of the speakers? Does it do it on all sources? Which tubes are you presently using?
I agree with Jjrenman. I would do a bit more isolating first. One of your other components could be at fault. Have you made any changes to your system lately? (New components, fixed something, moved the system, etc)