What to Consider When Buying Thermionic Valves

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What to Consider When Buying Thermionic Valves

Thermionic valves were used extensively in the first part of the 20th century, and though their use has waned with the invention of the cheaper, more easily manufactured transistor, they are still used in a number of specialised applications these days. For some people in the know, the transistor cannot compare with the life and feeling of a thermionic valve.

Thermionic valves, or vacuum tubes, are still used in a number of electronic applications, like transmitters. CRT computer monitors, and CRT televisions. It is possible to purchase thermionic valves in certain electronics shops, although an individual may have better luck online. Mass retail sites, like eBay, are a good initial choice to look for electronic parts like these. Since thermionic valves are used in such limited applications, they are not well known generally. Therefore, for a successful acquisition, a buyer should know the types of thermionic valves, features, and the options available for such electronics.

Types of Thermionic Valves

There are many types of valves available, as modern technology has come up with increasing numbers of uses for thermionic valves. Still, at the most basic, there are several that have to be considered.

Diode Valves

These are two-electrode valves, hence the name, though they are also called thermionic diodes. The two basic electrodes on any valve are the anode and cathode. The valve allows current to pass in only one direction, and is the simplest kind of thermionic valve. These types of valves are used as rectifiers, which are great for electronics using DC power.

Triode Valves

The triode has three electrodes, compared to the two on the diode, the addition of the grid electrode to the anode and cathode combination makes for more applications than just rectifying. Triodes are used in electronics to amplify signals; it is, in fact, the simplest form of valve used for this purpose. Triodes are poor at radio frequencies, but add one or two more grids, and the capability of the valve increases.

Pentode Valves

For the buyer working with audio signals and hi-fi, or high-fidelity sound production, the pentode was created. The additional grids added to the basic diode design increases its functionality in amplifier applications even more than the triode design.

The three valve designs mentioned here are simple and of little use to practical amplifier applications, apart from school experiments, but they hold the basic design in which practical thermionic valves can be found and on which modern electronics are based.

Why Buy Thermionic Valves?

The majority of electronics have moved on to use transistors in sound management and signal modulation. Discerning audiophiles, however, prefer thermionic valves in their audio devices. There are distinct reasons why one or the other may be used, however.

Type of Device



Thermionic valve

Superior quality of sound

Smooth clipping of signals is widely more musical sounding than transistors

More able to cope with voltage spikes

Not dependent on temperature

Higher operating voltages, therefore, wider dynamic range

Valves can be replaced with ease by end user

Bulkier than transistors, therefore, less portable

Higher power consumption

Fragile, especially when made of glass

More expensive


Cheap and more portable than thermionic valves

Less heat emitted

Less power consumed

Can be more efficient than valves

Greater safety for builders because of lower voltage needs

Often more durable

Higher amplifier distortion

Less efficient cooling

Needs more complex design to lower distortion

Can blow out easily with sudden increases in voltage

More difficult maintenance; not easy to replace

Basically, the reason for using transistors in mass-produced electronics is practical and wholly mathematical, in other words, they are cheap, easy to produce, and output sound that is good enough. Thermionic valves, on the other hand, are used mainly for the enhanced human experience, especially in sound and music production, which is why hardcore audiophiles often build their own audio devices.

Uses of Thermionic Valves

Thermionic valves, despite their decline in use over the last century, are still offered by manufacturers like Phillips and Mullard. Even now, they are used in a number of applications more mundane than creating particle accelerators and industrial radio; the most obvious example being the music industry.

Rock Music

The distorted guitar sounds in rock, metal, and punk, are not produced by the guitar alone. The amplifier is one of the more important components of the live act. Audio production uses, as mentioned earlier, triodes and pentodes. Overloading different triodes and pentodes produces even or odd harmonics; and these applications need increased voltage amounts. This is the reason amplifiers need to be grounded properly, or someone on stage could be electrocuted. Thermionic valves are used extensively in professional music amplifiers, especially those for heavy, scream-out-loud music.

Recording Effects

Recording experts do not use thermionic valves as extensively as people who produce music, but the devices are still needed to get a full range of effects from their effects boxes. When recording, people generally use valves to exert greater control on signals, like microphone channels where the singer may vary the proximity of their mouth from the mic, which results in somewhat uneven sound.

There are preamplifier kits for recording artists or engineers that contain valves; easy access for getting sound to filter properly from recording microphones.

High Fidelity Audio

Thermionic valves produce better quality sound than transistors and integrated circuits; it is no wonder music lovers gravitate to using them more often. For audiophiles, the only reason for using valves is that the music sounds better. This is certainly a consideration when a person is looking for ways to enhance the experience of listening to music. Valves can be used in any audio output device, like headphones, speakers, amplifiers, and more.

Digital Light Displays

Digital displays in clocks, DVD players, car dashboards, and more are often anodes that are phosphor-coated. The temperatures on the device are manipulated in order to make these filaments glow. Many of these devices contain thermionic valves.


One of the more perceived disadvantages of the thermionic valve is its bulk. Recent innovations have made valves small enough to be referenced in nanoelectronic applications. Valves are capable of handling greater power than integrated circuits made of transistors, which is why they are used in fields that need high power outputs and low power consumption, like smartphones, radar, satellite communications, and Wi-Fi transmission.

Buying Thermionic Valves on eBay

Thermionic valves can be acquired from specialty shops, although if such a shop is not available in your local neighbourhood, then searching for the items online can be more productive. Sites like eBay are go-to places for items that may not be available locally, because they bring together hundreds of sellers from different parts of the country. It is easy to do a search on eBay; simply navigate to any page of the site and type your keywords into the search bar. Typing "thermionic valve" into the search bar offers you a number of results in keeping with what you are looking for. You may also want to try "vacuum tubes" or "thermionic tubes". There are tools on the eBay site that help you filter out choices that you do not want, or arrange your list in order of price, condition, or distance from your location so it is simple to see the items that are most relevant to your needs.

As in every online and offline shop, remember to evaluate the product carefully and thoroughly before buying. Thermionic valves rarely cost much money, so brand new items are not a burden on a buyer. In addition, remember to check the seller feedback on the product listing page, as well as the seller's feedback score, in order to gauge their reliability.


When people think of thermionic valves, they think of early 20th century technology. But there are still thermionic valves being used today, because despite the prevalence of transistors and solid state devices, there are things that valves do better. Looking for thermionic valves can be hard if there are no specialty shops in the locality of the buyer, which is why online shops, like eBay, are particularly helpful. There are also specialty websites that sell thermionic valves, which can be a boon if retail sites do not pan out.

People in the business of recording and producing sound, the music industry, in particular, generally comprise a big percentage of those who still regularly using thermionic valves. Valves are especially valuable in the amplification and control of signals, in other words, they are great devices to increase the quality of sound in music. Thermionic valves are not that expensive, though they are more costly than transistors, so a buyer looking for a top-quality product is not forced to break the bank. Remember that electronics are delicate, though valves are more hardy to voltage bursts or electromagnetic pulses than circuits based on sensitive conducting substances, like transistors and integrated circuitry, they still can be smashed by pressure and force, especially as many valves use glass in their body.

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