What do you see as the downside of tubes?

I've seen a few mythologies espoused on this thread so maybe we can sort some out.

Triode-based amplifiers tend to have very consistent performance over the life of the tubes, which in general also lost longer. In this case, Krauti is considering a triode amp. Pentode tubes do degrade much faster, with far less consistent performance.

The idea of 'damping factor' is confusing and not helpful. It is certainly **not** required to produce deep, articulate bass with plenty of authority and slam. All speakers and amplifiers do not work together; if for example you think that because you have a solid state amplifier it will drive anything, think again. There are plenty of speakers out there that it will not be able to drive correctly, just as if you have a tube amp, there are plenty of speakers out there where the same applies. It is in fact a matter of equipment matching in all cases, see
http://www.atma-sphere.com/papers/paradigm_paper2.html for more info.

Heat: if properly designed, the components in a tube amp will last as long as they will in a solid state amp. Its as simple as that- otherwise we would not see vintage tube amps still in service after 50 years...

Also, it is a fact that class A operation makes for the best sound (all other things being equal that is), whether tube or transistor. So if we are talking about a tube amplifier, the heat it makes will be only slightly higher than a transistor amp that makes the same power. Granted, the heat **sources** are more concentrated in a tube amp, but for the record the difference between tube and solid state **if we are talking about class A operation** (and we are in this case), is only about 15%. IOW, the heat comes from the class of operation, not so much the device. Try running a transistor in class A with no heat sink and see how hot it gets (hint- it can melt plastic)!

Raquel, just a FWIW, we probably have as many tubes in our amps as anybody, but they are autobias and hold together quite well, even if a tube fails. Having a lot of tubes does not have to be a pain in the neck if the amp is designed properly.

Actually, Carver showed that an amp could be *modeled*, but even in his tests the modeling did not match the actual behavior of a tube amp.

Mapman, here are some primary differences.
1) Tubes are often much more linear than transistors. Triodes are the most linear form of amplification known. This results in far less need or no need at all for feedback to reduce distortion.

2) tubes produce mainly lower-ordered harmonics, transistors tend to produce higher ordered harmonics, especially odd-ordered. This can be easily seen in the overload characteristics of the amplifiers where these behaviors are exaggerated. Anyone who has run an amplifier into clipping and observed the output with an oscilloscope knows what I am talking about

3) tubes tend to high impedance while transistors tend to low impedance. In addition, there are capacitive effects in transistors that are magnified at higher currents. The effect of this is that both transistors and tubes will sound better (lower distortion, smoother sound, greater transparency) when driving higher impedances.

We put a Standby feature on our amps so that you could keep the amps warmed up 24/7 if you wanted to- and rated the amps accordingly. The nice thing about tubes is that if you want the system warmed up properly, it only takes about 3 hours, where solid state requires about a week. So IMO, why waste the energy- I don't run the amps 24/7 because I don't *have* to for best sound, though I certainly could and have done so many times in the past.

As proof of that I just came home from vacation and found that I had left my preamp on while I was gone. Sheesh- I hate wasting the power, but the preamp was none the worse for wear.

Anyway, if the tubes are in Standby (filaments but no B+), they will make very little heat (unless your amps use 6C33s). Most of the heat a tube amp makes is due to the class of operation, not the filaments. IMO if heat is what is the priority, your system is going to sound like it too. I would not call that a high end system- a high end system is all the stops out to create the realism and experience of music. To do that will make heat, tube or transistor not withstanding.

There is a common tendency to trade convenience for performance; digital vs analog and tubes vs transistors are examples of this tradeoff. If there was any way that transistors could be made to make the music that tubes can, I would not be making tube amps- but I put up with the base nature of tubes because also therein also lies the closest you are going to get to the music.

Eldartford, digital modeling amps have been around for years in the guitar world. As far as I can tell, people only play them out of desperation as they are a far cry from the thing that they are trying to model, i.e. a Marshall Plexi or Fender Twin. Its going to take more convincing than is possible in a thread to make modeling a plausible exercise for high end audio!

Mapman, not exactly. Pentodes are less linear in some ways than some CMOS devices, but still are more linear than a bipolar device. So the comment is a generalization, but only barely. In the case of triodes, there are no transistors, even the best fets and their variants, that are as linear.

Linearity in the device is a big deal if you want true audio/musical performance. Without it you will have to run less gain per stage and more feedback, making for a considerably more complex circuit. The simplicity of tube circuits is one of the ways that they rule over transistors.

Simple transistor circuits are rare. Their master is Nelson Pass. He has sorted out some of these simple facts, and built some of the best-sounding transistor amps around. But when you examine them, you will find that many of the so-called advantages of transistors (low output impedance, low heat) have been thrown out in favor of real advantages (performance that is musical to the human ear).

We ran tube-based regulation for years. I'm as a big a fan of tubes as anybody, but when we developed a proprietary regulator for high voltage, it was **immediately** so much better than the tube circuits that there was no going back.

There are a lot of factors in a regulated power supply! Essentially the regulators behave as a sort of power amplifier that you are listening to. They have to be very linear and wide bandwidth to really work right. The problem we ran into with the tube regulators is that bandwidth is a real problem. The result is right now that our regulators function with wide bandwidth and about 2 orders of magnitude less noise than is possible with tube regulators.

I'm not saying that tube regulation is all done in, but some innovation needs to occur before it can keep up with a **properly designed** solid state regulator.