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One of my Penta Labs kt88's has a crack in the glass. I've just noticed it and powered down the amp. The tube is still hot but it feels like a ridge protruding out of the tube. I've never seen this in any of my other tubes before. I am going to pull the other 7 and inspect them as well. I've included a couple of photos of this abnormality. Please look at them and let me know what you think. Thanks
Greg
Follow Ups:
I am an idiot. I tried scraping at whatever it was on the tube again and this time it came off. It was not a crack or anything, duh..
Cracked glass would not hold vacuum for any considerable time.
Im not sure what it is either. I tried to scrape it off with a razor but had no luck. It is definitely part of the glass envelope and I pulled all the tubes for fear of a failure. It protrudes off of the glass and feels sharp to the touch. I'm going to ask for a replacement just to be safe. I am hoping someone around here has seen something similar to this and can offer some advice.
Thanks
Greg
I should also mention that the crack was not there when I put the tubes in the amp. I must have 10 hours on them now and it occurred sometime today during the 6 hours it was on. It does not allow for leakage as the flashing is all still there but I pulled the tube just in case. Any thought on this?
I had a tube with a 1/4" envelope crack that didn't compromise vacuum...yet. I returned it.
Another time a crack developed that turned everything white within the glass envelope; found it after its amp channel had no output, having remembered hearing a dull "ping" when last turning the amp off. As an SE amp output tube it simply didn't conduct, and the amp was OK.
Can you inspect yours under magnification? Do cracks usually create surface protrusion?
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