Strange amp noise

[black mariah]

Maybe you guys can help me with this one. I have a Carvin X100B. All tube, 100 watt. I lent it to some friends and when I plugged it in earlier today I noticed a distinct hum coming from it. It sounds thinly metallic and gaseous, like when you tap a blown preamp tube, but I tapped all the tubes and there is no noise when I do. It is strong enough that I can feel it through the amp's cabinet. Not good. :cry: Could someone point me in the right direction? I know very little about tube amps.

[petemoore]

Not the same...drag...I monitor my tube amps when they're in use, that's just me   :?
 Safety First, I would take it in and have it lookedat if you're in any sort of rush to have it repaired, potentially lethal voltages in there.
 RG's GEO has tube amp info, and there are alot of links around, like Ampage etc.
 hAving spare tubes makes it easy to test the tubes...but,
 I try to repeatedly check for 'hot looking tubes if my amps actin' funny, if the metal starts glowing shut her down.
 Other than that it's follow the guidlines for debugging an amp...which for me, if that was the only amp I had and tubes didn't do it, and 'preliminary' tests don't identify the problem...taking pin voltages, tapping for loose connections with an insulator rod...changing caps just to see, and have newer caps in it...

[black mariah]

One thing I forgot to mention. It isn't buzzing or humming through the speakers. Everything sounds normal when I play through it. The noise is emanating directly from the head, even when it's on standby. How's THAT for messed up? :lol:

[petemoore]

Well that's not so bad...lol...at least you can use the amp, or guess you have run it for a 'while' [more than 20-30 minutes] and have noticed nothing other than it's head humming.
 I don't know enough about humming transformers to say good / bad, other than I've heard that before, so maybe it's 1/2 normal, ie the amp isn't self destructing and the performance is good. I wouldn't like it at first expecially...something makes me thing transformer...
 To isolate noise, run it through a solid shaft instead of through the air, a noisy bearing can quickly be confirmed as 'alternator or PS pump or water pump by 'poking a stick in your ear [gently] so that it contacts the skin over bone part [right next to the hole] then touch the stick to suspected noisy component, you'll be able to hear more clearly the sound the closer the stick is to the source. Do this on the non-wiring side of course. My guess is it's a transformer making that noise...not to unduly cause amp-paranoia, but could it be drawing alot of current?, do the houselights dim when you turn it on?