Thought I would make this it's own thread, and do a quick poll about this. I noticed in my Penncrest CTC-15 clone, when I pulled the 6BK4 out, it jingled. The used tube that came with the set also jingled when it was tilted. What causes this? I know tubes like the 83 have mercury inside, and those can jingle or appear to have metal inside them, but a 6BK4? In both cases, I was unable to see anything loose inside the tube. And both tubes worked (although one failed after about five hours of use)
Another AK'er commented that he noticed jingle in his tube. Is this something common to all 6BK4's? A common failure? Coincidence?
Inquiring minds want to know.
-Ian