To provide a little context for the site and explode some common myths I have drawn up a short list a "Frequently Asked Questions". If you have other questions you feel should be answered here, please email me at: email@example.com and I'll see if I can add these the list.
Yes - definitely! Thanks to my friend Adam for pointing this out :)
By the way, Adam is the guy who persuaded me to build a Hartley oscillator with the 1 kW GM100 triode and so he's not blameless in all of this ...
Good question, two part answer: In terms of mainstream consumer electronics and computers certainly yes.
In some specific applications no:
Valves are still used in commercial broadcast stations where huge amounts of Radio Frequency power must be generated.
Many people really like the "valve sound" for their Hi-Fi and electronic instrument amplification and so valve audio amplifiers have gained a definite main-stream following.
For the electronics and radio enthusiast, valves offer a chance to make some beautiful, functional and excellent pieces of equipment and possibly to engage in some serious nostalgia.
There are a number of enthusiasts collecting rare types of valves. Some antique or unusual types can command a very high price. Generally these devices will not be used but will be displayed (one hopes).
Yes. Businesses such as Eimac make power valves, some devices being able to generate more than 1 mega watt of power. Smaller valves are manufactured by Russian, Eastern European and Chinese firms.
Huge quantities of New Old Stock or "NOS" valves are still available. These are valves that were made years ago but have never been used and are often still in the original packaging - assuming this hasn't rotted!
Because there are valve amplifiers and radio equipment in use today, a number of retailers are active in providing good stocks of valves for sale to individuals.
Contrary to popular belief valves can actually last quite a while. All valves do have a finite lifetime but this lifetime can be measured in thousands of hours for many parts and so can perhaps they should be regarded as "service items" rather than just plain unreliable.
Power valves do wear out over time and broadcast types are generally replaced according to a strict schedule to ensure total equipment reliability. Low power valves (often called receiving valves / tubes) will generally last a very long time unless they "go soft" (air gets in or gas gets out of the metal parts inside) or the filament breaks due to mechanical or electrical fatigue.
The life of low power valves is thus mainly dependant on the quality of manufacturing and their subsequent treatment. Many types can exceed 10's of calendar years of moderate usage in well designed circuits. For example, my 1955 Pye radio has all but one of it's original valves in it.