Sunn sonaro distorting ?
 

My sunn sonaro amp is distorting when I turn the volume past 4? 1st time it does this

check your valves, if one of your power bottles has gone it's ussually a symptom of this

Valves meaning tubes?

Is it the 40 watt combo amp or the separate head version?
If you have a Sonaro, it's 40+ years old. When was the last time the filter caps were changed out?

Ask at the Sunn Discussion Page, lots of friendly, truly knowledgeable folks with lots of vintage Sunn experience there.

It's separate, head and cab

If it hasn't been serviced, I would say a whole bunch of things going a bit wrong.

The entire head was rebuilt but still original tubes

The tubes I know are old but until 2 days I was still getting a good sound

"Entirely rebuild" can mean a lot of things.

Yes indeedy... ;)

Do you have the old parts that were replaced? If so, post a pic of them, that should tell the story pretty well.