[mark funk]

Hello, My HiFi uses a few tubes all the same kind, 12AT7-ECC81. Would like to know what happends to the tube when it's rings? I have a few NOS tubes of many types. I use Telefunken in all my stuff both ECC81 and ECC801s. I put a pair in my pre amp (810s) and both tubes were ringing ( I though that kind of odd both?) So what has happend inside the tube for this to happen?


                                                                                                         

[FullRangeMan]

My 2 cents are:
If you mean said ringing=hi microphonic, I suspect it caused by vibration of the inner tube elements, or much resonance on the chassis/tube socket, coming from the transformers or speakers.

[hifiman5]

Have you tried any tube rings that are designed to absorb vibrations coming through the chassis into the tubes?  If not, you might check out Herbie's Audio site and look at the wide variety of tube dampers that might help with your concern.  Email Steve at Herbie's and he'll advise you on how to work with your particular situation.