tube amp/flutter in speakers?

Just a note: For those that think that DC will cause a driver to throw forward and stay in that position, that is not necessarily correct. The DC level could be fluctuating up and down. As such, the driver would move forward, but could appear to "flutter" or move in and out as the amount of DC voltage varied. It would never take a "full stroke" ( positive push forward and then the accompanying negative stroke backwards ) as that would represent an AC signal. DC would only move in one direction but could be moving or fluctuating none the less.

One could actually play music over the top of this, but you would have to present a higher level of AC voltage ( music signal ) to the speaker than the DC level that was leaking into it. The higher AC voltage would actually "muscle" the speaker into moving, but it wouldn't be near as sharp, clean or clear as if there were no DC present. Needless to say, there would be a tremendous amount of heat build-up in the speakers' voice coil and "melt-down" could occur. In severe cases, the driver will literally "flame out". I've seen this happen at rock concerts. The unknowing crowd simply thought that it was "special effects".

Further damage to the amp could also occur, as there is a drastic amount of reflected voltage fed back to the amp in a situation like that. The speaker is resisting movement due to being partially locked in place by the DC so some of the AC music signal is not absorbed and sent back to the amp.

Keep in mind that it is also possible for a driver to "suck in" or move backwards rather than go forwards when DC is present. This would have to do with the polarity of the DC voltage and how it is connected to the speaker. Sean
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Are you sure its not the components upstream from the amp? You can check this effect by simply removing the input connections from the amp, and unplugging all of the gear that is upstream.

I have seen ground loops / ground problems cause this...

If it is the amp -- it seems like a power supply issue -- this may happen due to a bad diode, regulator tube, or capacitor. There are certainly other things it could be - these are the most common ones I have run across...

Good luck -- and follow Sean's advice if you can't quickly figure it out...

Unless it's a rare output transformerless (OTL) design, your amp has an output transformer between the power tubes and the speaker. This transformer will not pass DC unless it is seriously defective, in which case you'd likely have more severe symptoms such as smoke and overheated output tubes.

If it's not coming from an upstream component, then as mentioned above, low frequency oscillation is the likely culprit.

I agree that it's time for a trip to the shop.

Ghostrider, don't believe the old wives tale about transformers not passing DC. It's a lie. They will pass DC, just not anywhere near as effectively as they do AC. Sean
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Sean, was that a KISS concert or AC/DC where you so the flash out of the speaker?