What to Consider When Buying Vacuum Tubes

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What to Consider When Buying Vacuum Tubes

Vacuum tubes, in modern times, are most popularly used in audio applications, especially in the creation of high-fidelity (hi-fi) sound. Many people in the recording industry use vacuum tubes or valves. Guitar players are also especially concerned, as they use vacuum tubes to enhance and manipulate the sound created in their amplifiers.

There are not many vacuum tubes manufactured these days because most of their use has been taken over by transistors and integrated circuits. Still, there are a number of shops that sell these items. A buyer would be better served to search for these tubes online, as most brick and mortar electronic and music shops do not think it worthwhile to stock a very good selection. Understandable, since demand is limited to a small number of the population. The eBay site is one of the better online sources for quality tubes.

That said, searching for the right tubes to use in an amplifier or in recording equipment can be a little complicated. Knowing the different features and options available for various vacuum tubes or which vacuum tubes ideally serve for certain situations and equipment, helps the buyer make decisions that end in satisfactory results.

Type of Vacuum Tube

There are many types of vacuum tubes still available for different kinds of applications, most still in the audio business. Vacuum tube type names are usually combinations of numbers and letters. Names for the same vacuum tube or valve can differ in different parts of the globe, for instance, the European ELL80, which is a tube that used to be installed in ancient Fisher hi-fi amplifiers now goes by the name 6HU8 in the United States. Below are a few other examples.

6JS6, 6KD6, and 6LF6

These are three of the bigger-sized television line output driver valves, also known as "sweep tubes", though there are many that are used in applications outside of television sets. They are generally used for the same thing and have similar fixes, so they are lumped into the same category. For example, they are all used in amplifiers for CB and amateur radio applications. Like most sweep tubes, these are rare, and therefore, on the higher side when it comes to cost. It is possible to modify the amplifier to take EL509 or EI EL519 from the company SED in Russia, though the modification needs rewiring and new parts.

6SL7GT and 6SN7GT

These are dual triodes used in preamps, although the 6SN7GT offers medium gain and is still used in some modern hi-fi applications. There are still companies that make the two at present, so a buyer does not have too much trouble looking for them. The 6SL7GT is a better choice when looking for high gain on amplifications, although unlike the other, this version was generally used in hi-fi and guitar amplifiers that were created before 1956.

12AT7 and 12AU7

These are also preamp dual triodes, but they are more common than the 6SL7GT or the 6SN7GT. These can be found and used in more hi-fi and amplifier sets or builds. Because of that, they can sometimes be less expensive than others. The 6201 is a special version of the 12AT7 that offers better high-reliability audio. The 12AT7 is also called the ECC81, and the 12AU7 is also called the ECC82. Most vacuum tubes have alternate names, and modern versions of old NOS tubes can have similar names, but with an added letter or number.

12AX7

This is the audio preamp dual triode that a buyer is most likely to encounter. An example is the Telefunken smooth-plate ECC83, which was used extensively in hi-fi applications, although it is now scarcely found, and if seen, is often very expensive. The Telefunken brand of this tube type is one of the best versions. There are Mullard versions of the 12AX7 also available. Many Chinese-made examples of this type of vacuum tube can be seen, but a buyer should know that Chinese and Russian brands are generally considered of low-quality for tubes. Still, there are some types of tubes that are only made in these countries.

300B

A popular power triode for individuals who care very much about the quality of sound coming out of their hi-fi amplifiers is the 300B. It is more often than not used in single ended circuits, although it can be applied to other uses. There are several companies that make the 300B, which is a good thing since it can be used in places of several rarer vacuum tube types, like the 275A and the 252A, with minimal adjustments to the amps. SE amplifiers that normally take the 50 type tube can also be modified a little to take the 300B. Note that the 300A is an earlier version of this vacuum tube and is identical, at least electrically.

7199

This is a triode pentode, one of the smaller ones. It can be found in older amplifiers, like the Dynaco Stereo-70 amp. There are modern versions of this vacuum tube available at various tube dealers.

Brands of Vacuum Tubes

Other than the type of vacuum tube for which to search, the brand is also an important matter to consider when trying to buy vacuum tubes, especially since vacuum tubes are scarce, and more often than not, expensive. Not all brand names are compatible to a hi-fi application and not all would do as well as another. The following brands have been the most popular, and are generally known to offer superior tubes.

Origin

Brands

American brands

RCA, GE, Sylvania, Ken-Rad, Dumont, Tung-Sol

British brands

Mullard, Brimar, Mazda

Dutch brands

Amperex, Philips

French brands

RTC

German brands

Telefunken

There are other companies that make vacuum tubes, but these are considered some of the best. When looking for tubes that provide great quality, then these ought to be the first choice. It does not mean that other companies and brands should be discarded, of course. Note that these are some older brands that may or may not be in production at present. There are other companies that produce more modern types of vacuum tubes.

New Old Stock (NOS)

It is impossible, when looking for vacuum tubes, not to hear about NOS tubes. These are vacuum tubes that have been created when tubes were very much still in demand and have been stockpiled away. They have never been used, despite being created maybe decades ago, hence the term new old stock. NOS vacuum tubes are generally considered of higher quality, and are often preferred by audiophiles over tubes of modern production.

Real NOS tubes have never been used. Many offerings in the present market are used tubes, or like new. Determining if the NOS tubes being purchased are one or the other helps the buyer get the full worth of his or her investment. Most of the better NOS brands are mentioned in the table above. Check the listings or advertisements thoroughly for these brands. Most sellers test their tubes before sale. If the description says that the tubes "test like new", then they are probably good enough to buy even though the tubes are used.

Buying Vacuum Tubes on eBay

It is a bit difficult for the audiophile to acquire great quality vacuum tubes, as they are sold mainly by specialty shops that are few and far between. Searching online may be the best option for the buyer. The eBay site is one of the best places online to find items that are difficult to acquire in physical shops. It helps that the site is easy to navigate. You simply have to type the keywords for what you are looking for into the search bar on any eBay page. Simply typing in the words "vacuum tube" gives you a large selection of choices. These choices can be narrowed down by using the site tools to filter out the kinds of tubes that you do not need.

It is also possible to narrow down the listings by being more specific with your keywords. Note that vacuum tubes are also called valves, thermionic valves, and electronic tubes. When looking for the ideal tube, note that the tubes should have been tested by the sellers. It is an excellent choice if the seller uses tubes too, so they know how to answer your questions well. Also, check whether the courier or shipping company is reliable. Vacuum tubes have glass parts and can be delicate. Reputable shipping companies take that into account, not to mention they probably ship faster.

Conclusion

Many vacuum tubes today are used in the audio industry, which is why it helps if the person the buyer acquires the tubes from has similar hobbies, like listening or playing music. They should then know whether a tube is working properly or has some slight defect. A guitar amplifier, for instance, usually uses a 12AX7 or 7025 but sometimes there are special circumstances and a person with firsthand knowledge of vacuum tubes knows how different tubes work in various applications and can give the buyer indispensable advice.

If a buyer is trying to acquire NOS tubes, always check that the listing says they have never been used or that they test like new. Still, there are exemplary modern vacuum tube brands made that do very well even without the quality reputation of NOS. Specialty shops are nearly the only places to acquire vacuum tubes, but buyers have more choice canvassing Internet sites. The eBay site is one of the more popular Internet haunts for rare and hard to find items, and it is an excellent starting place in the search for tubes to amp up top-quality sound. Always make sure the dealer or seller is reputable and knowledgeable. Of course, a bit of research into vacuum tubes serve the buyer better than going into a shop or ordering an item blind.

 
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