tube vs SS preamp

There is very little danger of a tube preamp failure causing a large signal that would take out a speaker, particularly when the downstream amp is a low to medium powered tube amp. Damage is more likely with a solid state amp, particularly higher powered amps.

Tube linestages can be a bit more prone to non-life threatening noise issues than a solid state linestage, but, most of such issues can be cured rather easily by changing noisy tubes. As far as life expectancy is concerned, this is largely a matter of the design of the linestage. Most small signal tubes used in linestages have long expected lives and are usually run conservatively and will last a long time. However, there are some designs, such as those by Counterpoint and Audible Illusions that were run somewhat hot and needed relatively frequent tube changes.

I generally prefer an all-tube setup to one that is a hybrid. But, I have run solid state into tubes with pretty decent results. I have generally found the alternative hybrid setup--tube linestage into solid state amp--to be less predictable and consistent in result; it can work, but, there is a greater chance of the combination being a disappointment.

I have never never witnessed, either personally or among the many friends with tube gear, a failure of tube gear that lead to damage of a speaker. Most tube failures end in distortion or no sound from the speaker. In a post above, someone mentioned problems with DC being sent to the speaker; this is impossible with most tube gear because an output transformer CANNOT output DC--DC in the primary would mean no output from the secondary because a fluctuating magnetic field (not DC) is required to induce a current in the secondary. The only possible DC from a tube amp would involve an OTL that does not employ a protection circuit or a blocking capacitor, and I have been told that that failure mode does not happen much either. I suppose that ANY high powered amp, tube or solid state, has the potential to do damage from a failure or operator error causing high level noise to be passed into the speaker.

On the other hand, I have been witness to a few solid state "failures" that did do in speaker drivers. Most often this was caused by operator error (e.g., accidentally pulling an interconnect from a source component causing a LOUD pop). I have also witnessed damage from just plain old abuse of playing at excessive volume--much more common with solid state gear because high power from solid state is "cheaper" and more common.

Owning tube gear might mean a bit more effort is required to maintain top working order--testing and replacing tubes, cleaning tube sockets--but, damage to speakers IS NOT one of those concerns. I would be MUCH more nervous if I owned high-powered solid state gear because of either failure or other conditions that can cause very loud noise, such as power outages/fluctuations (I've heard near heart stopping thumps from solid state gear when power flickered off and on because of crappy service in my area).