Tubes question??

[gatom21greyhound]

My Stiletto was making noise last week right before I shut it down. When I went to turn it on it wouldn't go on. I noticed that 3 of the 12ax7 tubes had a white milky top to them? Any ideas what could has caused this?

 

[212Mavguy]

That white looking top is a sign that there is no more vacuum in the tube, those are ruined. Usually means that the bottle has been cracked or broken. Time to go tube shopping.

 

[crane]

That white looking top is a sign that there is no more vacuum in the tube, those are ruined. Usually means that the bottle has been cracked or broken. Time to go tube shopping.

+1

 

[Timbre Wolf]

My Stiletto was making noise last week right before I shut it down. When I went to turn it on it wouldn't go on. I noticed that 3 of the 12ax7 tubes had a white milky top to them? Any ideas what could has caused this?

There has to be more to this story, as 12AX7 don't just spontaneously, simultaneously lose vacuum - something has to crack their glass. Did someone throw a beer bottle or something? I suppose sudden, extreme temperature changes could also cause this. Besides replacing the dead tubes, I urge you to find out what the cause was.

- T

 

[fishyfishfish]

Call Mesa and see what they say. I ran my Lonestar with two bad tubes and didn't notice until a third went out. When I went to get my spare, one of the spares had a white top.

 

[MrMarkIII]

This is evidence of mechanical failure, i.e., the amp was dropped, or dealt a physical blow of some kind. A tube amp is basically a box full of light bulbs and should be handled as such.
Hope this helps.