Dc voltage sent to my speakers

@mulveling is correct in all counts.

The amplifier transistors swing the output voltage between 0 and one of the two power rails (plus and minus).  Anything from bad input, to a shorted transistor along the way could cause the output voltage to stick to the rail.

Fortunately you can use a voltage meter to check this.  Set it to DC and measure the amp outputs with no speaker attached.  First with the preamp off.  If you have more than a few millivolts it's probably the amp.

Can you share what amp and preamp you were using?

Most solid state amps have a protection circuit to prevent damage to the speaker in case of output section failure (which is how they typically put out DC that can damage speakers). So this is a bit unusual!

Most solid state amps have a protection circuit to prevent damage to the speaker in case of output section failure

Um, not the one's I've seen especially "high end" amplifiers that pride themselves on not having any.

It varies a lot by make and model IMHO.  I've seen plenty of schematics with just fuses and an anti-oscillation circuit on the outside.

@mulveling  , forgive me for my limited ability to understand electrical theory, but based on what you typed, assuming the applicable cap failed inside a tubed preamp, the output transformers of the tubed amp (assuming a tube amp was behind the pre) would still protect the speakers from DC voltage?