2. amps-preamps
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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.

thx!
jc51373
newbee
4,822 posts
 
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.
jc51373 OP
548 posts
 
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.
jw94055
125 posts
 
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.
mechans
3,048 posts
 
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.
unclejeff
1,313 posts
 
Are your interconnects/speaker cables anywhere near your power cord? Also, try changing power cords.
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