Let’s talk about Vacuum Tubes
Audiophile Heaven your one-stop source for rare high quality new old stock vacuum tubes and valves.
All our tubes are checked for Shorts, Emission, Life test, and Leakage before shipping.
We test on vacuum tester and valves testers like:
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Amplitrex AT1000 Advance Digital Tube Tester, USA
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Hickok 752a tubetester, USA
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AVO Type 160, UK
What is a Vacuum Tube?
A vacuum tube, also known as a thermionic valve (or simply a tube), is an electronic component that controls the flow of electric current in a high-vacuum environment inside a sealed glass or metal envelope. It was a fundamental technology in early electronics, especially in amplifiers, radios, televisions, and computers, before being largely replaced by solid-state devices like transistors. The operating principle of an electronic vacuum tube is similar to that of a hydraulic valve. Electrons travel along electric wires or vacuum space, in place of water flowing in pipes. The electric potential (or voltage) forces electrons to traverse electric wires and vacuum space, in place of the potential energy due to the effect of the gravity pushing water to flow through pipes. Finally, an electronic valve can control the flow of electrons, analogously to what described for hydraulic valves.
Below are the basic types of electronic vacuum tubes and their operating principles.
Diode
The simplest type of electronic vacuum tube is the diode. A diode has two terminals: a cathode and an anode. When the cathode is sufficiently heated, electrons start to leave its surface, due to the thermionic effect. When an electric potential V+, higher than that of the cathode, is applied to the anode, the electrons emitted by the cathode, which have a negative charge, are attracted and move toward the anode itself.
By convention, the direction of the electric current is that of the “positive” charges. Therefore, even if the electrons move from the cathode to the anode, we say that the electric current goes from the anode to the cathode. In fact, a current of negative charges in one direction is equivalent to a current of positive charges in the opposite direction.
Triode
In a triode, a third terminal, called grid, is placed between the anode and the cathode. When the electric potential of the grid is lower than that of the cathode, the electrons emitted by the cathode are repelled and find difficulties to reach the anode. If the grid is negative enough, current is blocked, obtaining the same effect of closing the valve in the hydraulic circuit. If the grid potential is the same than that of the cathode, the current flows freely from the anode to the cathode, obtaining the same effect of fully opening the valve in the hydraulic circuit. Intermediate negative grid voltages modulate the current flowing from the anode to the cathode. When a voltage signal is applied to the grid, the electric current, from the anode to the cathode, follows the signal applied to the grid. It is important to note that no current traverses the grid in normal operations. Being the grid negative, with respect to the cathode, it repels electrons and there is no electric current.
Tetrode
The basic idea of the triode was refined with the introduction of the tetrode. A tetrode, has a fourth electrode called screen, between the anode and the grid. The screen has the purpose of reducing the capacitance produced by the grid and the anode. In fact, in a triode, the grid and the anode are very close one to the other and jointly behave as a small capacitor, which might cause instability and oscillations. If the screen has a voltage higher than that of the cathode and the grid, but lower than the anode, it acts as an electrostatic screen between the grid and the anode, thus reducing their inherent capacitance.
Tetrode in ultra-linear configuration
In a tetrode, the screen is positive with respect to the cathode. Thus, it attracts a certain amount of the electrons emitted from the cathode itself, which would have gone to the anode. The result is a small current flowing through the screen. This effect is exploited to configure a vacuum tube to work in distributed load, or ultra-linear modality. This configuration is obtained by feeding back a percentage of the anode output signal to the screen, rather than applying a fixed voltage to it. The wanted percentage of anode output signal is typically provided to the screen by connecting it to a tap, coming out from the output transformer. The current through the screen, produces a sort of negative feedback and, with the appropriate percentage of anode signal, distortion falls at very small values, just slightly reducing power efficiency. The optimal percentage to be applied to the screen depends on the specific electronic vacuum tubes used. In many power amplifier designs, this percentage is generally set around 43%.
Pentode
Tetrodes were further refined with the introduction of the pentode. When electrons emitted by the cathode reach the anode, they might have enough energy to stimulate secondary electron emission from the anode itself. Secondary emission electrons might reach the screen grid, causing instability and oscillations. In order to prevent secondary emission electrons from reaching the screen grid, pentodes use a fifth electrode, called suppressor. The suppressor is generally directly connected to the cathode, either with an internal connection in the vacuum tube, or by an explicit connection between the corresponding pins.
What do the numbers and letters in a tube's name mean?
There are several different tube numbering systems that you may see on tubes, which generally are a result of where they were built. Most commonly the numbers contain digits only (e.g. 5751), or are some combination of numbers and letters (12AX7, ECC83, CV4004). These different numbering systems may be from the American or British military, or from American or European industrial or consumer use, and then of course there are many strange exceptions. But to use the notation commonly seen in the United States, here is the meaning of "12AX7":
12 - the filament voltage
AX - an arbitrary model number
7 - the number of internal elements, including the filament
To make things more complicated, many tubes have letters after the name, such as 6L6WGB, 6L6GC. Sometimes these letters mean functionally nothing (design revisions) and sometimes they refer to different voltage capabilities of a given type.
The bottom line for buying tubes for your amp: we list types together that will work in your amp without problems. There are many different tube substitution possibilities for those wishing to push the limits in the quest for unique performance.
Why do some types have many different names?
As mentioned in the answer to the previous question, some types (usually the popular ones) are referred to by different numbering systems. For instance, what is a 12AX7 in the U.S. is an ECC83 in Europe is also a 7025 to Fender owners because for a while Fender sold tubes labelled 7025 that were a low noise 12AX7. These tubes are all the same thing.
Does any tube that fits in the socket work okay?
No. If you aren't sure why some weird tube is in the clearly labelled socket of the amp you just bought, ask us or pick up a handbook and check for yourself. There are thousands of tubes with identical basing, and the vast majority of them won't work in your amp.
Why are some old types more expensive than others?
Mostly, it's supply and demand. These tubes aren't being made anymore, and lots of vintage amp owners like to have a purely vintage rig, tubes and all. Also, much like vintage amplifiers and guitars (or vintage tuners and stereos), certain items achieve anointed status and their demand is even higher than usual, which also pushes the price higher.
Are new tubes from Russia and China as good as old tubes?
Yes. No. Maybe. This is one of those questions that answering can be problematic, because the answer is up to your ears. There are many good tubes being produced right now, and every company in the business has had difficulties with certain types. This has led to a bum rap for an entire industry that works very hard to reproduce tubes from "the good old days". It's also true that people with a garage full of vintage tubes tend to think they sound better, no matter what they hear. Most modern amps are designed around current production tubes for the good reason that they know you will be able to re-tube your amp in the future, and so these modern designs tend to sound best with current tubes.
How often should I change the tubes in my amp?
A simple guide is to replace the power tubes twice as often as the preamp tubes, because they wear out more quickly. An amp that is used every day should expect to replace its power tubes every one or two years. If you notice lower output, strange noises, or a "muddier" tone, your tubes probably need replacing.
What does "JAN" in a tube name mean?
The JAN designation is found on many American made new old stock tubes, and stands for "Joint Army Navy". It means they were originally built for the military, often with improvements in their construction and quality control.
What is "New Old Stock"?
Commonly known as "NOS," New Old Stock simply refers to tubes that were made years ago but have never been used. Much like antiques, "NOS" tubes are currently not being manufactured and this means their supply is dwindling while the price continues to rise. We have over 1000 NOS tube types available. We have a few specially selected NOS tubes available as NOS Treasures.
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