How to Buy Thermionic Valves on eBay

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How to Buy Thermionic Valves on eBay

Thermionic valves redefined audio electronics over 100 years ago and are still defining audio performance for many audiophiles today, especially musicians who use amplifiers. These classic bits of technology are still coveted for the unique sound they bring to amplification, despite the invention of other technologies, including solid state amplification, in the last several decades. Guitarists in particular often sidestep alternate technologies and enjoy using these essential pieces of technology to add unique colour and life to their amplified sound.

One of the larger resources for thermionic valves available to consumers is the online auction site, eBay. The site aggregates vendors to create a diverse catalogue of options for those in the market for thermionic valves. Learning how to find and purchase these tube amplification devices on eBay can open up a wealth of resources for audio enthusiasts or anyone looking to buy a thermionic valve.

Buying Thermionic Valves on eBay

The online auction site eBay is designed to facilitate a quick and easy purchasing process. When you first visit the site, you can find a search bar at the top of any page on the site. This interface gives you a user-friendly way to begin exploring listings related to thermionic valves. All you need to do is enter an appropriate search term and click the ‘Search’ button. Of course, before beginning the purchasing process, you may want to make sure you have an understanding of these items, including their main applications, the way they work, and their most common varieties.

What is a Thermionic Valve?

A thermionic valve, referred to by people in North America as a vacuum tube, is a device which uses a vacuum in a sealed, cylindrical container to control an electric current. The first thermionic valve created, the diode, essentially has the structure of a basic filament bulb, using a cathode with the addition of an electrode also known as an anode. As the cathode element heats, electrons release from its surface and make the added electrode or anode more positive than the filament or cathode, creating an Edison effect or thermionic emission.

Modern Applications for Thermionic Valves

Thermionic valves are still used widely by musicians who use tube amps and some vintage radio and electronics buffs. Despite the advent of solid state technology such as transistors and semiconductors, which can be easier to use and more reliable, many audiophiles prefer the sound quality produced by a thermionic valve or are dependent on them due to the design of an electronic device.

Thermionic Valves in Music

Thermionic valves are used in both performance and recording. Electric instrumentalists, in particular, are devoted to tube-based amplification and the sound of an overdriven tube amp has defined the sound of Rock n Roll for decades now. Whereas a solid state amp can clip when overdriven, a tube amp compresses the sound naturally, creating a unique tone distortion. Many instrumentalists also credit thermionic valves with giving amplifiers a warmer and richer tone. Attempts to digitally replicate the sound of a tube amp have not been tremendously successful, allowing the thermionic valve to retain its title as the go-to item for electric instrumentalists.

Vintage Valve Radios

Thermionic valves are also used to repair and optimise vintage valve radios. Tube technology drove the creation and engineering of radios from 1914 until the beginning of the 1960s, making thermionic valves essential in the upkeep of almost any vintage radio.

Types of Thermionic Valves

In addition to the diode thermionic valve, there are several other types of thermionic valves which build upon this basic structure. Additional electrode elements, called grids, are added into the basic diode structure to enhance the performance of the valve. The following chart lists the name of each type of thermionic valve, as well as the number of additional grids and total anodes in that specific valve.

Valve Type

Number of Grids

Total Anodes



















The basic concept of the vacuum tube outlined here enables signals to be rectified and amplified. Many refinements have been added in the form of further grids to enable a much better performance to be obtained, but the principles involved are all the same.

The Thermionic Valve Numbering Systems

There are several numbering systems used around the world to define an individual thermionic valve. These systems usually incorporate a series of letters and numbers that represent various characteristics of the valve, including its structure, its base, and its filament. Consumers shopping on eBay may encounter any one of several numbering systems when looking for thermionic valves.

Mullard Philips Tube Designations

The Mullard-Philips system is widely used in Europe and defines the majority of thermionic valves created in Europe since the mid-1940s. In the Mullard-Philips system, the first letter denotes the heater or filament voltage type; the second letter and up to three letters after that describe the device's structure in detail. These letters are followed by a series of numerals which describe the valve's base type. For special quality valves, the letters 'SQ' may also be included or the order of the letters and numerals after the first letter may be switched.

The following chart lists the definitions for both the heater voltage letters and the structural definition letters used within the Mullard-Philips system. With regards to the base type, the numbers 30 to 39 indicate an octal base, while the numbers 80 to 89 and 180 to 189 indicate a noval base.

First Letter - Heater Voltage



4 V


180 mA


200 mA


1.4 V


6.3 V


12.6 V


5.0 V


150 mA


2.0 V


450 mA


300 mA


100 mA


50 mA


600 mA


Cold Cathode

Second Letter - Structure



Signal Diode


Dual Signal Diode




Power Output Triode


Small Signal Tetrode


Small Signal Pentode


Mixer Hexode


Mixer Heptode or Octode


Power Output, Beam Power, or Pentode


Fluorescent tuning indicator


Gas-Filled Thyron




Power Rectifier Diode


Dual Common Cathode Rectifier Diodes

These charts can help consumers determine the type and structure of most European thermionic valves on eBay. There may also be valves on the site which are defined by other international systems. Consumers should communicate proactively with a seller to determine the compatibility of those valves with their needs.

A Note on NOS Valves

When shopping for valves on eBay, consumers may come across a phrase that may cause some confusion. This term is 'NOS' or 'new old stock.' This phrase is used to refer to stock which is unused but is a make and model that is no longer in production. Many classic thermionic valves from past eras can be found as NOS items. Keeping an eye out for NOS stock can help lead consumers to items that are in great working order and ready to integrate seamlessly into a device.

The Purchasing Process on eBay

Once you have familiarised yourself with some of the specifics of thermionic valves and know how to identify the types of valves you can come across on eBay, you can begin the purchasing process on the site in earnest. After you run your initial search, begin reviewing individual listings in detail. Look for information on the valve itself, as well as purchase-related information such as delivery cost and payment requirements. All of these details can help you determine whether a particular valve is right for you.

Getting to Know the Sellers on eBay

During the purchasing process, you should take some time to evaluate and get to know the sellers carrying thermionic valves you are interested in. You can do this by clicking through to the seller's page, then by clicking on the highlighted seller name on the listing's page. On the seller's page, look through the past auctions that seller has conducted and review customer feedback submitted by others. You can also consider communicating directly with a vendor to confirm specific technical or purchasing details before finalising your purchase.


Thermionic valves are highly valued electronic devices which are still widely used by an array of individuals, including audiophiles and instrumentalists. These individuals are always on the lookout for valves to replace existing valves or upgrade the performance of an amplifier or other electronic device.

As an aggregator of various electronics vendors and independent sellers, the online auction site eBay offers a large catalogue of these electronic staples. By taking the time beforehand to understand the basics of thermionic valves and their designs, as well as the numbering system used to log these valves, consumers can leverage eBay's wide-ranging set of listings and make an informed decision when searching for these tubes. With its user-friendly interface, eBay gives consumers a quick entry point to the purchasing process. After taking a moment to review listings and vet any associated sellers, consumers can utilise eBay to find the ideal thermionic valve to enhance a radio, amplifier, or other electronic device.

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