Tubes... what do they do?...

I would say it is a matter of taste what different types of amplification moves you. I would say tubes lends a small degree of realism to the reproduced music. You can mention that you have a tube stereo to average individuals and you will be looked as an excrentic, until you play some music.

It produced this warm, soothing glow that takes your mind off of the cares of life, and your system, as it ever so gracefully distorts the signal to its final output. Not exactly what you would call a tube fan, but I have done some research conducted by independent sources and historical periodicals. Once you understand what you are reading as far as charts, specs, and graph; and apply this to to the overall effect of the systems performance, you come to this same conclusion.

Let it be known...my opinion completely differs from the concensus of this thread and its contributors, and doesn't represent the opinion of audiogon. :)

Transistor amps generally have a very linear transfer function (until they clip). Transistor amps generally have a more 'S' shaped transfer function meaning that for low amplitudes, the gain is higher and for higher amplitudes, the gain tapers off. This can give the impression of more low level detail.

Some strange comments here.

Vacuum tubes are amplification devices, and tubes like the 243 or 300B are the most linear open loop amplification devices known to man. The proof of this is that you actually get vacuum tube power amplifiers that do not make use of any form of negative feedback, and those that do, use very little NFB.

Transistors have very high open loop distortion levels, which need be addressed by using negative feedback loops. The use of negative feedback (in both vacuum tube and transistor) in amplifier lowers distortion levels.

Opinions differ pertaining to the use of negative feedback, as it does introduce non-harmonic (i.e. phase) distortion, which many folks find disturbing. Distortions associated with vacuum tube amplifiers (with little to no negative feedback) are mostly a diminishing amounts of first, second and third harmonic distortions which many find pleasing to the ear.

Harmonics occur naturally with all sound waves i.e. strum a single guitar string and the other vibrate in harmony; so an amplifier with a high level of harmonic distortion can still sound extremely lifelike and real (because it is). Phase and inter-modulation distortion do not occur naturally, so even very small amounts can give the music a cold or hard edge and sound very unnatural.

Good amplifiers (and bad amplifiers) can be had using either vacuum tube or transistors. Anybody that simply dismisses one topology as being bad or distorted is simply demonstrating ignorance.

Regards
Paul

So Pauly...what testing results or guidelines do you use or suggest one should use to determine the difference between a good tube amp and bad tube amp? How should one inteprete the tangible results of the testings?