The great Tung-Sol tube failure mystery

[Marcel]

I've been following this thread with every post, and only just now gone back to the original picture and enlarged it.... Hmmmm...

Sad to say but this looks suspiciously like a batch manufacturing fault.... The fault being an incorrect join between the base glass (that holds the pins and subsequent metal work) and the sleeve glass envelope. There are two possible causes being either a/ the weld was not done correctly with the most likely issue being the join was not hot enough to melt the two glass pieces together, or b/ the two pieces of glass are of slightly different composition and thus have slightly different expansion rates hence leading to cracking when the tube is operated normally.

Looking in particular at the 2nd tube how the base section is so fractured my guess would be the second option where the glass used on the base was not manufactured to the correct specification required... Yes it is glass but not the correct type of glass...

I'm still going with my original comment on claiming warranty, particularly as you have 3 almost identical failures. Sticking with Tung-Sol or not for the moment ... Hmmm.. I don't know. You might get 3 new ones from the same batch, or 3 from an entirely different batch...

[RalphH]

Just a thought, has the amp ever been in transit recently?, ie, being transported from one place or another?, also, was the amp recently moved from a warm environment to a cold one after it had been powered down after use?, that can sometimes end in tubes cracking.

None of that... been in my music room for 18 months. Average temp 16-25° over 12 months winter-summer. Just popped the lid and stuck the Tung-Sols in. Finished a 2 hour session last night with the old 7025's installed without a problem. Hmm...