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

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?

11-16-06: Cdwallace “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?”

Use the most complex and most accurate audio evaluation devices known to man - your ears.

As a bit of an education, have a look at http://www.high-endaudio.com/. Arthur is somewhat opinionated, but has a wealth of knowledge and experience and you may just end up learning something.

Thanks Paul. I also found this doc to be useful as well, back when I wanted to research the anatomy and function of a typical SET amp. This also includes many of the scientific strategies and practical analysis of the tube amp, which also produces tangible conclusive results.

http://www.next-power.net/next-tube/articles/Cheever/cheever.pdf

I must admit, even though I'm not a fan of tube amplification, this document was very eductional regarding the practical applications many of today's tube amp manufactors use to test their products before release to the market.

This is just one of many available. I'll see if I can find more and post them.

I'm glad to see there is more than one person who is into education regardless of how much experience one has.

Good looking out Pauly! : )

Enjoy!