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
Craig, It sounds like you have done enough to rule out a faulty tube as being the source of your problem. That said you are really going to have to have a tech diagnose and repair the problem. If you did not buy this from a dealer I doubt that Deal is going to repair it. He wouldn't work on one of my units which I bought second hand. He did, however, refer me to a tech in the LA area to whom I sent the unit and had it repaired promptly and at a fair price. These units should be easy service so if you have a tech in your area who knows tube amps you could probably have it done locally.
This might be stating the obvious, but are you sure the amp is designed to work with KT150 tubes?  Either way, it might be worth trying it with the stock EL34 and see if the problem still exists.
Craig, this isn’t hard. Just call PrimaLuna / Upscale Audio. They will help you. 
  @mickeyb
Sell it now. Seems everyone else is. You see how many are for sale?
Yeah, check out the prices. If you find a good one it's only $1000-$1500 below list. Most used equipment goes for 50% or less. The Dialogue Premium series has been superseded by their new EVO series of balanced amps, I notice that many have just gone up for sale. I'd sell mine at $1000 off so I could buy the new ones. That's a good deal for me!

Have you talked to the person who sold it to you? They may be of some help or stand behind their sale and assist in it's repair.

Rollin