Tube Amp Hum

I have a new VTL ST-150 for about two weeks now. Its breaking in nicely, but one thing I notice with this amp is a slight hum through the midbass drivers. Not audible from the listening position, but there nonetheless. I have the amp on a dedicated 20 amp circuit which was quiet as a mouse with the SS amp that was on it before this amp, which eliminates it being a ground loop. Also, all tubes are all seated properly.

So my question is, is this a normal operating characteristic for a tube amp? If so, does it have a degrading affect on the sound? I would like to hear just pure air when my equipment is on like I had before if possible.

Some light humming from a tube amp with your ears at the speaker is not unusual. Some are dead quiet, some are not. Occasionally it can be from tubes or currect. You might try a cheater plug and see if that changes the hum (I assume all of your stuff is not on the same line (?). You might also check your connecting IC's to insure they are not too close to other electrical devices, including the amps themselves and power conditioners etc. If you can't hear the hum when you're standing a few feet from the speakers it shouldn't really affect the sound, except mentally by us anal types. :-)
Thanks Newbee...Yes it is when I am at the speaker only that I can hear it, not from the listening position which is only about 8 or 9 feet away. I moved my ICs around a bit and there was no effect whatsoever, and they are shielded (97% according the manufacturer).

The sound is definately not that famous buzz noise which is usually associated with ground loops-which I have chased in the past. This is more of a hum, like a current flowing noise (IE transformer). Also, when you power this amp and the room is quiet you can hear it's initial draw. Kinda like a faint wuuuuunnnnnnhhhuuuuuunnnnhh noise. Bad description I know, but hopefully that describes it.

Outside of listening AT the speaker there is no noise, but where I am new to tube amps and experienced with SS this noise is new to me. If this is normal I can certainly live with it because the amp sound phenomenal. I just prefer to hear that delicious airy sound when my equipment is powered up.
Depends on the efficiency of the speakers
Correction now that both my wife and I listened for it. It seems louder out of the left channel than the right, and....It is faintly audible from the listening area, not just at the speaker.

I gotta tell ya, if there is way to resolve this noise I would love to know. I am not one for noises of any sort from my audio system.
I know this sounds left field, but try different cables from your pre to power amp. I have a tube pre and ss power. I bought some high end cables and they produced a buzz. Replacements were tried with the same result. Put in old generic cheapos and the buzz went away. I would make sure the shielding on the interconnects is plenty thick. Again, this is one person's suggestion.
Could it be from your cable tv provider? Many have had problems with cable tv and stereo system using the same eletrical lines...Or possibly your refrigerator...Just 2 thoughts.......Good luck
Reverse the tubes - and see if the sound follows the change or remains constant. Reverse the small tubes first - if the left channel is still a bummer, try the power tubes next. If that doesn't help call VTL. I have amps which hum a bit, but its the same in both channels - so if its not the tubes it may be a bad part in the amp which needs to be replaced.
My refrigerator? Definately not....The system is on a completely dedicated circuit, there is no cable system on this circuit whatsoever. It is not a ground loop.

Newbee, I will try the tube reversal as you mentioned. Sounds like an idea.
I echo and emphasize the fact that some tubes have a high noise floor. Try different tubes. Also some trannies, but first and foremost are the tubes. I have an all tube set up.
Are your interconnects/speaker cables anywhere near your power cord? Also, try changing power cords.
Heres a theory...I have Herbies Audio Lab isolation feet, which have a good reputation and I am pleased with them. But...Is is possible that because they are squishy material, the transformer hum noise is being trapped inside the amp and coming through the speakers?

Just a thought, maybe its stupid but thought I would throw it out there.
I have tried cheater plugs, different circuits, moving the amp to a slightly different location, reversing the input tubes and the hum is still there.
In addition to the above mentioned, does a cable TV box share the same outlet or AC line? Also are your interconnects unshielded? Is your preamp tube or solid state? I purchased a new tube rectified preamp a while back to use on a solid state power amp and I was never completely able to eliminate low level hum, only reduce it but it sounded good enough to overlook. If overly concerned you may want to contact VTL in California. Congrats on your new VTL amp, an excellent choice!
Thanks Phd, its a tubed Pre. A 2.5 soon to be a 5.5 in about 2 weeks. The line the audio system is on is dedicated to it, not cable tv on the same line at all. Cable TV near it, but no connected in any way whatsoever. The cables I have are shielded (Nordost Frey) 97% according to the specs on the Nordost website. Although I am going to try some other interconnects at some point just to eliminate them as a possibility. The ICs have a tendency to be very sensitive in general so it is a possibility I guess.

My feeling is this is just simple and honest transformer hum, and nothing more. But I still think I need to go through the steps of eliminating everything else as a possibility.
My brand new ARC VS60 has what you describe. Same in both channels. I have a feeling this is how it goes but left a message with ARC. I'll see what they have to say. I hope it can be eliminated. My solid state amp was dead silent.