Microphonic feedback?

Hi All

I am hoping you can help. I am running a tube integrated and a subwoofer amplifier to drive the second voice coil of my Gallo reference 3.1s. In this configuration when I turn up the volume of the subwoofer amplifier enough to activate the second voice coil/subwoofer I get a terrible bass feedback which quickly overwhelms the speaker and room. This does not happen when using solid state amplifiers. I think it might be tube microphonics ??. 
Any help or guidance would be most welcome.

Thanks in advance

An extreme case if so, but it could be. Especially if your speakers and amp are not isolated in any way. Townshend Pods under the tube amp will probably be the best solution. Not only eliminate the problem but give a big improvement in clarity and truth of timbre. Huge. Did under mine.

I had a very similar problem only with my turntable on springs, where certain things would excite the right frequency into feedback and it was horrible. Townshend Pods under the turntable not only eliminated this entirely they brought about a really nice improvement in everything else as well. That is why they are now under my amp, phono stage, and Podiums under the speakers.

You could also use Podiums under the speakers, but I would start with the amp as that is a whole lot easier and cheaper. Or if you want a really cheap solution Nobsound springs. They are not nearly as good or worthy of your system but they do work and would be a great test for not much money.
Thanks MC, I’ll order some to see if that’s the ticket. I also wonder about tube dampers...?? Any thoughts?
What makes you think the feedback is related to amplifier tube microphonics? If you tap on the amp’s tubes, does it send an impulse thru the speakers?

Are you using a turntable for a source? If so, that’s the most likely origin of your trouble.
Hey Cleeds,

inpoint to the tubes as it doesn’t matter what source I am using, and this problem does no occur when I have my solid state gear in play.