Cracks on RFT preamp tubes....

  • Thread starter Thread starter apophis
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apophis

Well-known member
A guy on ss.org posted about small cracks on the bottom of all his rft 12ax7 tubes....so after checking mine it seems it also has some...now i dont want to pull out the ones i have installed in other amps since they might break...can you guys tell me if these cracks are normal on these tubes, or do they happen for a specific reason?i am always careful with all tube handling
 
I just happened to have my stash of 15-20 RFT's out (expecting a new amp today and going to roll tubes in V1), when I read this. Wide variety of different brandings on most, and cannot find any cracks or stress fractures in the glass bottoms near where the pins exit.

Perhaps the guy on SS.ORG bought a damaged batch, or mishandled them........or maybe I have just been really fortunate!
 
the cracks are really hard to see...i used a magnifying glass, and tried to tilt them so light highlights them..... my tubes also show the cracks going from the center of the base to the pins, thats why i was asking, it seems like a weird coincidence. At first i did not see them..
 
I've got a handful of RFT ecc83's and a couple have what looks like small stress cracks like your describing . I 'm constantly rolling tubes and haven't spoiled any RFT's yet. I did have an old Raytheon black plate go bad but it had a half moon crack at the base.
 
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