New Prima Luna Amp In Distress / Me Too

Prologue II 40WPC Integrated – (4) KT-88s (2) 12AX7s (2) 12AU7s. The amp arrived new six weeks ago and has maybe a bit over 200 hours operation. Today, sequences of double popping began coming over the speakers. About a second between each pop then after a minute or so another double pop. There was no input signal at the time.
I switched the input selector from phono over to CD and the popping continued.
I then played a CD and noticed a gain and fidelity increase in the middle of the pops (the short sequence). I then noticed that the blue glow from one of the KT88s increased within these short bursts of fidelity/gain that were bracketed by the pops as well.
I shut off the amp and let it cool before swapping tubes to see if the problem followed the tube or was dedicated to that socket. When the amp was powered back up, the popping was gone but both middle output tubes (the ones that were swapped) did not come up to full blue glow and a good part of the bass section has fallen through a trap door in the soundstage – and remains that way. It is now off line. I’m ready to box it up and send it back for warranty work. One note – this amp has a proprietary on-the-fly auto biasing circuit.
Anyone who can explain what’s going on will have praises sung by me until my dying day. I’m heartbroken!
Vm8444, I've already mentioned the tubes I prefer in the One...nuff said. However, if you do some checking I think you will discover that the SED EL34's are a Mullard copy and the EI's are a Tele copy. These are inexpensive new production tubes and I recommend them highly for what they are, without regard to the Prologue One. But, if you've got the money to spare, that NOS recommended to you might float your boat as well or better.
thanks newbee,,loving my prima one,,currently still using stock tubes ,,but I am getting the itch to roll,,maybe the cv4004 mullards,,and maybe slvania 12ax7 ,,then we'll see about output tubes later ,,thanks bro.
It’s been a few months since the original faulty tube has been swapped out with a replacement KT-88 sent by Upscale Audio. Things sailed along smoothly until last week when another stock KT-88 tubes began popping and demonstrating the same problems.
After checking with Kevin at U.A., he suspected it might be vashode powder. On close examination, this turned out not to be the case (at least, as far as I can tell).
At any rate, since this latest intermittent failure began in the same socket as the first one, I’ve decided to replace the entire power set to rule out any “hot seat” factor that might be emanating from the amp while it’s still under warranty. I’m going with Valve Art Kt-100s which are a rugged Chinese copy of the old Genolux design KT-88.

Whether this ends up to be just an unlucky set of stock tubes or a problem with the Luna, I’ve come around to thinking that this may be the challenge that one sometimes has shoulder in tube audio.

It should be noted that Kevin reports that, outside of a few PL Kt-88s demonstrating a similar problem with Vashode powder (none in the PL-EL-34s), the Prima Luna Amps are demonstrably good builds with few problems. In fact, I’m not in a panic about all this – learned a lot about this amp through troubleshooting – learned also that when it’s on song, it’s absolutely warm and lush and competes with the best of ‘em.
Tell me more about the blue glow? I know this is an old thread.
I want to see it.
In summary blue gaseous glow in power tubes is good, and pretty. Lack of it is neither unusual nor indicative of anthing bad to come.

For a detailed explanation of the reasons go to Audio Asylum and look at their FAQ's. I'm too lazy to explain.