Subwoofer rumble issue

years ago I lost a bass unit on a rega jura. The combination of TT, room, track and record warps led to a loop that saw the drivers very quickly oscillate more and more until the paper cone literally tore open around the center area, this took less time than I could get over and turn the volume down....the other driver survived the experience, I don’t think the voice coil burnt out but somehow the extreme excursion caused the cone to rip.

Hey George - tubes seem to be ok. I’m running the Phonomena II through the aux so I’m assuming the preamp tube(s) in the amp aren’t being utilized, right?

Where and in what are these tubes situated, if in a tube preamp (model?) and your using the aux input you are still fully using the output buffer tubes of the preamp, but you say they seem to be ok?
So then I'm affraid we come back to the air-born feedback.

Cheers George

big_katydid
The combination of TT, room, track and record warps led to a loop that saw the drivers very quickly oscillate more and more until the paper cone literally tore open around the center area, this took less time than I could get over and turn the volume down

Yes, this is another way the air-born  runaway feedback oscillation can start. The wrap was the initializer, then the air-born takes over and just runs away getting louder and louder till something goes bang! 

Cheers George

The tubes I checked are in the CM II integrated. 4 power tubes, 3 12AU7s and 2 12AX7s. I’m running the Phonomena II+ phono pre which is solid state. I assume some of the small tubes in the CM II are still being utilized in the signal path - I believe the center position 12AU7 is the Preamp tube.