Seems possible that your amp shut down when it detected some DC from your pre-amp. Can your amp do that? Not unusual situation when tube pre-amps are used to drive SS amps.
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Ralph, Are you saying that it doesn't happen? Or that it is just rare or unusual? All we might be talking about is our definition of what constitutes 'not unusual' v 'quite unusual'. If the latter then what I suggested remains a possibility, does it not?
BTW, assuming the fuses in the amp did blow wouldn't you want to know what caused them to blow in the first place?
Hell, maybe all of this stuff about DC is moot anyway. Perhaps the problem is that something failed in the pre-amp and caused the fuses in it to blow. Note the OP did mention the smell of 'burn' (something I've smelled several times when a cathode resiter in the bias circuit of an tube amp sacraficed itself when a power tube blew out. Until I noted that his amp was SS I thought that was what happened. I have have no knowledge of this amp).
FWIW, I have nothing to sell, opinions, comments, or stuff. Was just trying to start a dialogue with the OP about his problem. Sorry if I stepped on your toes. Since you are an expert I will turn this over to you to handle. I'm sure you can solve the problem more efficiently than I ever could.
Newbee, no worries on this end. Most tube preamps have a coupling cap at the output that prevents DC. Failure in such parts even after 30-40 years is really rare. So DC at the output of the preamp is not likely to be the issue.
I agree that DC at the input of a SS amp could bring serious issues, although most SS amps have protection for that. Given that things just 'died' though, my recommendation is just check the fuses- all of them, including those in the preamp.
Another thing to try would be to disconnect the interconnect from the rear of the preamp and see if the amp will make a buzz in the speaker. The fact that both channels died is significant- whatever causing this is common to both channels. That is one reason why I reject the preamp DC argument- if a preamp *were* to pass DC, its far more likely to be from one channel than both.