tube amps sounding like solid state and vv

FWIW the underlying mechanism here is called negative loop feedback. It is a design device that is often used to reduce distortion. The problem is that in doing so, it is not perfect and actually *enhances* certain odd-ordered harmonics that the ear uses as loudness cues.

These artificial loudness cues are detected as 'hardness', 'harshness', 'brightness' and the like. Negative feedback can be used by both tube and transistor preamps. Those tube preamps that use it to excess will likely get a reputation for sounding 'solid state' whereas the careful transistor preamp designer can get his preamp to sound 'tube like' by limiting the use of feedback.

Component choice can affect things too, so its tricky to ascribe things entirely to one source. But in general you will find that feedback has a high collerlation with 'transistor sound'.

Typical tube circuits have very few components in the signal path, and are therefore much more transparent than SS designs. Victor Khomenko of Balanced Audio Technology has simplified the circuits of BAT's SS units, re-thought/re-designed their power supplies and helped them achieve a level of transparency/liquidity equaling that of some of the best tube designs. Well worth the audition. I'm a die-hard tube lover, and using his VK-D5 CD player, but- still a fan of his SS design philosophy.

There is an openness of sound that tubes are capable of that transistors have not yet achieved.

The only real downside to using tubes in amplification devices is related to driving lower impedance speaker loads (4ohm and below). In a preamp, tubes can drive the high input impedance of a power amp, which is typically 20,000 to 200,000 ohms, quite easily. There is also no need for an output transformer in a tube preamp. All of this means that the preamp is an ideal place to take advantage of the sonic benefits of tubes with no real downside.

The best tube and solid state preamps are attempting to converge on the theoretical definition of neutrality, but they probably never will because it doesn't likely exist.

I'm a firm believer in the notion that the pre-amp is the better application for tubes rather than the power amp.

Mapman, it depends on the speakers. For example, something like a 16 Ohm speaker load might be better served by a tube amp.