PRIMA LUNA DIALOGUE PREMIUM - 20 minutes and then loud pop and buzzing in 1 channel


Hopefully someone can help.

Amp is virtually new. The amp will operate wonderfully for 20 minutes and then a loud pop , and then buzzing from the right channel. I shut down the amp and then it repeats.  I switched some tubes and it is still there.  I switched the cables and know for sure it is only one channel, the right one. The buzzing does not increase with the volume increased. . 
It is the amp and not the Prima luna preamp.  Cables and connections are fine.   Pushing Focal Kanta No2's . 

Any help would be very much appreciated. I'd rather not send a 68 pound piece of equipment through the mail. 

Thanks lot - Craig 

128x128vespacraig1966
could be tubes, could be caps or anything. I heard a popping noise like that on my guitar amp it was a preamp 12au7. On my hifi was an old telefunken. I have to recap the whole amp. My lesson is I gotta have a backup amp in a situation like this so I bought a used solid state. Its not the same but at least it got me by and got my amp done the right way. Now it sounds like thunder!
Sell it now. Seems everyone else is. You see how many are for sale? It was on my short list until recently. Hope your fix is simple. 
Sell it now,seems everyone else is?..So you suggest dumping it on someone else and taking a huge loss..stupid comment at best.Prima luna makes very good products,ive had several.
"Sell it now. Seems everyone else is. You see how many are for sale?"

Listings on Agon,AA,USAudio-ZERO

Perhaps this poster is being facetious? I've used PL products for years without problems,along with many others
Hopefully, it is something simple. Doesn't look like the OP has completely eliminated a bad tube.