There are plenty of people that drive Maggies with tube amps. I agree that tube microphonics would explain what you are hearing, and it is pretty easy to address. Also, the fact that you tried two other speakers, one of which gave you the same result, probably means it is not the Maggies per se. However, because they are dipoles, they may direct more energy back to the tubes. Just wondering, the other speakers you tried--- were they both rear ported? If the one that didn't give you distortion is front or bottom ported, or sealed, that could also be a clue.
On the other hand, I had no such problem with my 3.7s with my Coincident Line stage preamp, which uses highly microphonic 101D tubes, and had no problems, although I do use tube dampeners.
It might also be worth switching out the speaker wires and ICs if you have spares. A weak connection at the terminal can give intermittent distortion problems.
On the other hand, I had no such problem with my 3.7s with my Coincident Line stage preamp, which uses highly microphonic 101D tubes, and had no problems, although I do use tube dampeners.
It might also be worth switching out the speaker wires and ICs if you have spares. A weak connection at the terminal can give intermittent distortion problems.