I really doubt it.
First, because if the tube had leaked (silver getter turned white) then it couldn't sustain any current from the cathode to the anode, and so your DAC would have no output on that channel.
Second, you would have heard something nasty out of that woofer before it went bad if it was being overdriven.
Have you reversed your speaker cables and sent them to opposite speakers just to make sure that the problem is indeed with that particular speaker and not something else upstream?
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First, because if the tube had leaked (silver getter turned white) then it couldn't sustain any current from the cathode to the anode, and so your DAC would have no output on that channel.
Second, you would have heard something nasty out of that woofer before it went bad if it was being overdriven.
Have you reversed your speaker cables and sent them to opposite speakers just to make sure that the problem is indeed with that particular speaker and not something else upstream?
.