Usefullness of tubes

[GlenSify]

Hi all,

I am new here and a n00b when it comes to t00bs (sorry, couldn't resist) and I'm wondering about their utility in today's silicon world. I have been looking into building my first valve amplifier and have come to understand through my reading that the desirable sound quality of the valve amplifier stems from the "soft" roll-off of the gain as opposed to the "hard" clipping that occurs with transistors. It would seem to me then that the usefulness of valves is primarily in sound production - the domain of guitarists (among others) driving their amplifiers deliberately into distortion as they play. I don't know of an occasion when anyone would deliberately drive an amplifier involved in sound reproduction into distortion. Thus the question - why a valve amplifier?

[planet10]

That is only a small part of the reason. A good triode is still the most linear amplification device invented by man.

dave

[Wavebourn]

If a tube has at least anode and heated cathode, it can rectify. But if it has a grid between anode and cathode, it can amplify!

[GlenSify]

Sold, thankyou for the reply. Is there a resource which will provide a quantification of the comparative linearity of transistors and valves?

[rknize]

Originally Posted by GlenSify

I don't know of an occasion when anyone would deliberately drive an amplifier involved in sound reproduction into distortion. Thus the question - why a valve amplifier?

They don't do it deliberately, they just do it. It's part of sound reproduction (especially analog sources) to occasionally go into overload, even when not playing anywhere near full volume. There is also the issue of how your speakers' impedance changes over the frequency band. If the impedance dips way low, say from 8 ohms down to 1 ohm, that can push the amp into overload even when it isn't pushing that hard at other frequencies.

The key is how does the amp react (does it generate a lot of high-order harmonics due to the sharp cutoff) and how does the amp recover (from feedback loops and blocking distortions). Tube amps aren't automatically immune to these things, either. However because many tubes can be setup in a circuit to operate very linearly without lots of (or any) feedback, they can be very accurate and very stable and actually sound better than a transistor amp in cases where the tube amp is only rated at a small fraction of the output power. Cheap transistor amps need a lot of headroom to prevent these overloads as much as possible, so you need many times the power output capability even though you are only using 1 or 2 watts on average.

That's not to say a transistor amp can't be made stable either, but they typically just aren't unless you pay big bux. Often their own power supply isn't rated anywhere near what is required to reach the claimed output power of the amp. The key to a good chip amp is a good PSU...an expense most manufacturers aren't going to bother with.

[planet10]

Glen,

A new members posts are under moderation for a short period (usually 5 posts or so). Patience is sometimes required. I deleted your duplicate posts.

dave

[Jen-B]

It seems that if you want to amplify voltage without a lot of additional things (global negative feedback, temperature drift, servos, etc.) then an appropriate tube can do the job well. However impedance conversion is another matter!!! 'Horse for courses' I think.

[kavermei]

For completeness, I'd like to add that in some areas, there are no viable substitutes for tubes even today. If you have a microwave oven at home, it contains a special type of vacuum tube called a magnetron. I'm also thinking of industrial-scale induction heating, very high power RF finals, and large radar installations.

[Luke]

Ive not had alot of experience with valves, but in my experience it depends on the music you listen too. If you like easy listening vocal, jazz etc tubes are good, if you like rock solid state is good. Would tube affecianados agree with this?

[SY]

I have been looking into building my first valve amplifier and have come to understand through my reading that the desirable sound quality of the valve amplifier stems from the "soft" roll-off of the gain

Five minutes with a tube amp and an oscilloscope will convince you that this is not true.

Would tube affecianados agree with this?

I wouldn't, no. I listen to rock about 20% of the time and much prefer using tubes there, too.