Faint noise coming from tube area

[esteban]

My Prima Luna DiaLogue One integrated amp is making a faint "hissing" noise that seems to be coming from the power tube area/sockets. The noise is only audible if I place my ear very close to the tubes themselves, and not from the speakers or from a short distance. The best way to describe the noise would be like that of a CD spinning inside a player.

This amp has been rock solid, dead silent and problem-free so far.

Could this be a bad tube, or one that's about to die? Could one of the tubes be producing the noise, or do you think I have reasons to believe the noise originates from the amp itself?

[jdandy]

Esteban.......This may be a premonition. Perhaps a new PrimaLuna HP is calling.

[DonBattles]

How many and what types of tubes are being used? Do you have any spare tubes? Have you tried to remove and reinstall the fuses at different locations.

[esteban]

Originally Posted by jdandy

Esteban.......This may be a premonition. Perhaps a new PrimaLuna HP is calling.

Dan, I would love to, and have in fact given that amp some serious thought. My main concern is heat. 8 X power tubes, plus 6 X small tubes... in a small room, in South Florida... listening 5/6 hours a day... Today it feels like 96 over here. And it's only going to get worse in the Summer. You get the idea!

[esteban]

Originally Posted by DonBattles

How many and what types of tubes are being used? Do you have any spare tubes? Have you tried to remove and reinstall the fuses at different locations.

Since I just got new speakers literally a week ago, I decided to experiment with some power tubes this past weekend. I was using a quad of EH 6CA7's with my previous speakers, and I liked that combination a lot. I like it as well with the new ones, but for the hell of it I tried EL-34's (stock Chinese tubes, came with the amp when new) and Gold Lion KT-88's (pretty much on their last legs by now... love the sound, hate the failure rate and the price). So I went back to the 6CA7's, which I am currently using. These have about 5 months of gentle use. I do not want to swap any more tubes at the moment to avoid any potential "loosening up" of the parts/sockets. Maybe that is what is causing the noise? It is very, very faint. NOT audible through the speakers. Only when I place my head/ear against the amp itself. Maybe this is normal? Under most circumstances I would describe it as such, since most audio/video components I have owned in my life do generate faint noises to some degree or another. I spoke to Jared at Upscale Audio (Prima Luna USA distributor) and he said this is "normal electrical noise". But this amp has always been DEAD silent, and that is why I found it strange. Sound is great, however. Nothing seems to have changed there.

Apologies for the lack of a more detailed description. I am basically a tube noob. This is the only tube amp I have ever owned.

[esteban]

... to add to my post above... If I had to be more specific, I would say that it sounds like the power tube/socket area is "leaking air", if that makes sense...

[AudioNut]

This is what often happens when a power vacuum tube starts leaking air . . . .






And, You'd better get your equipment ready - just in case!

[esteban]

Forgive the ignorance, but can a power tube really "leak air"? If so, how?

I appreciate the humor, but would love to get to the bottom of the issue.

I did notice, though, that the noise is intermittent. I kept the amp on for about 4/5 hours today, with music playing in the background while I worked. Every 30 minutes or so I would get closer to the amp, stop the CD, and listen. Most of the times the noise was gone. Other times it was there. Again, very faint, very subtle...

I also noticed one of the tubes has a VERY slight blue flame inside. Coincidence? Culprit?

As a tube newbie, your insight is appreciated!

[jdandy]

Esteban.......The tubes have a vacuum inside the glass. There is nothing to leak out. If the tube somehow developed a leak, which is highly unlikely, it would draw air into the glass envelope and the tube would fail.

Depending on how many times you have had the different power tubes in and out of their respective sockets you could possibly have a loose pin connector in one or more of the tube socket holes that might be causing a slightly arcing that's causing the noise you hear. I have experienced that on a tube integrated amplifier before.

This can be repaired easily. Unplug the amp, remove the power tubes, then using a narrow pointed awl or ice pick and a flashlight to see down into the pin socket holes slide the awl on the outside of the metal socket connector to slightly bend it tighter. In other words, make the pin connector inside the socket hole have a slightly smaller diameter opening. When done, reinsert your power tubes, power the amp and hopefully if it was arcing making the noise, it will have ceased. I have successfully done this repair more than once on several tube sockets without any issues.

[esteban]

Originally Posted by jdandy

Esteban.......The tubes have a vacuum inside the glass. There is nothing to leak out. If the tube somehow developed a leak, which is highly unlikely, it would draw air into the glass envelope and the tube would fail.

Depending on how many times you have had the different power tubes in and out of their respective sockets you could possibly have a loose pin connector in one or more of the tube socket holes that might be causing a slightly arcing that's causing the noise you hear. I have experienced that on a tube integrated amplifier before.

This can be repaired easily. Unplug the amp, remove the power tubes, then using a narrow pointed awl or ice pick and a flashlight to see down into the pin socket holes slide the awl on the outside of the metal socket connector to slightly bend it tighter. In other words, make the pin connector inside the socket hole have a slightly smaller diameter opening. When done, reinsert your power tubes, power the amp and hopefully if it was arcing making the noise, it will have ceased. I have successfully done this repair more than once on several tube sockets without any issues.

Dan, thank you very much for the feedback and for pointing out the possible root of the problem. I am not much of a DIY'er, but will definitely look into the above and see if I can get to the bottom of the it. I would say that, all in all, I have swapped power tubes no more than 10/12 times, tops, in a period of 5 years. But the Prima Luna positively encourages "tube rolling", so I would assume that I am on the "conservative" side on that front, and that the amp is built accordingly.