Eden WT800B noise issue

[Tim E]

I have an Eden WT800B and I haven't used it for ages as it has an issue with a slight distortion overtone that creeps in as the note dies away. I have taken it to an amp repair place and they couldn't find a fault. There is no problem with the headphone out so I am guessing it has something to do with the power amps but the tech said the biasing was fine.
I was just going to get rid of it but I plugged it in again recently and it sounds amazing apart from this issue.

Has anyone had this problem or know of a solution?

Thanks
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[Treb]

Preamp tube still OK?

[Tim E]

[quote name='Treb' timestamp='1494171417' post='3293761']
Preamp tube still OK?
[/quote]

Yes, I've tried two different new tubes and it's still the same.