Lamp,
In terms of listening, tubes do clip "softly" whereas the solid-state amps generate a nasty hard distortion. However, if you view the output of an amplifier on an oscilloscope, monitoring the waveform as the amplifier reaches its output limits, a tube amplifier is just as capable of flattening the waveform as a transistor amp. It's just a more gradual escalation towards distorting the waveform.
As the waveform becomes more "clipped", it begins to approach DC, which is what will damage voice coils of any driver.
Alan
