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Types of Tubes

Welcome to my home page. This web site is dedicated to vacuum tube fans around the world. It is hoped to be both a place to buy, sell, and trade vacuum tubes, as well as exchange information on tubes. So feel free to email,or write your ideas, comments, and suggestions. This site will be constantly under development so check back often for new ideas.

You can exchange information about vacuum tubes and their uses at Simply email and your ideas and comments will be emailed to all members who have signed up on this list. So, sign up today on this vacuum tube email list! Exchange ideas, information, projects, links, and anything related to vacuum tubes.

Vacuum tubes are the best means, in my opinion, of amplifying and reproducing sound. Once you have heard a stereo system built with tubes, you really can't go back to solid state. The sound is so life-like, at times it seems real. A renaissance in vacuum tubes is currently under way. What was once thought of as old technology, is making a comeback bigtime. So if you have old tubes, don't throw them out. They may be useful, and maybe even worth big bucks.

Tubes produce predominantly even-order distortion in amplifiers, whereas solid state gives odd-order distortion.The former is much more pleasant to the human ear.In fact, some people like even-order distortion so much, that to them that is the characterstic sound of tubes.In addition, the basic purpose of transistors is to act as switches, whereas tubes are designed to amplify. This makes a difference in terms of application.

A tube amplifier of 40 watts may sound as loud as a solid state amp of 60 or even 80 watts. Tubes impart certain sound and musical qualities which transistors do not. There is no such thing as an amplifier which imparts no coloration to the sound, so if tubes impart more pleasant attributes than solid state, then one might as well listen to tubes,given a choice.

Once you accept the superiority of tubes in audio design, the next question is what types of tubes. The New Old Stock(NOS) tubes are in very high demand now because among tube connoisseurs, they have the best sound and reliability. Some of the brands which are most sought after are Mullard(UK), Brimar(UK),Telefunken(Germany), and General Electric(USA).

NOS tubes are bought and sold now like fine collectibles, simply because there is a finite supply available(they are no longer manufactured) and over time they will burn out with use(hence the available supply will shrink). So now is the time to collect them, because once the supply is gone that's it - there will be none left, and the price will only go up like a fine wine.

Some tubes have become so scarce, that a given sample may go for as much as $US 1,000-2,000. Now that's big bucks for one tube,especially when you consider that in it's heyday, the tube may have sold for only a few dollars. That's what I call inflation!

NOS Tubes For Sale

Great Tubes At Super Low Prices

5AR4/GZ34 Mullard UK. Military version of this tube. Is labelled CV 1377. Probably the best 5AR4 ever made. Very ruggedly built. Very hard to find in England now. Over time will become even more scarce. Buy now before it's too late. $73.99 SOLD OUT!

5AR4/GZ34 RCA labelled. Manufactured by Mullard in UK. The exact same tube as a Mullard labelled one, but carries the RCA label. In original RCA box. $73.99 SOLD OUT!

6BH6 RCA USA. Black plate. D-getter. Beautiful construction. Very rare. $19.99

6BN6 General Electric USA. Military version. Is labeled JAN. Made in Owensboro, Kentucky. Get them while they are still available. $12.95

6L6GC General Electric USA. Beautiful tube. Well constructed and durable. A classic. Get them while they are still available. $53.95 SOLD OUT!

7199 JAN Sylvania USA. Military version(JAN="Joint Army Navy") Perfect for older amps like Dynaco ST-70. Rare to find. $33.99 SOLD OUT!

12AT7/ECC81 RCA USA. Black plate. Beautiful tube in terms of sound and construction. In original RCA boxes. Rare to find. $19.99 SOLD OUT!

12AT7WA/ECC81 Mullard UK. Latest and last version. In white boxes. These tubes are excellently manufactured and sound like a million bucks. Very rare. $25.99 SOLD OUT!

12AT7/ECC81 Mullard UK. New style Mullard logo. Labeled as ECC81,with BVA(British Valve Association) designation printed on tube. In original blue Mullard boxes. Very rare. $39.99. SOLD OUT!

12AT7WA/ECC81 Mullard UK. Military version. Labeled as CV 4024. New style Mullard logo. Super quality in a military version. Very rare. $30.99 SOLD OUT!

12AT7/ECC81 Mullard UK. Military version. Labeled as CV 4024. Old style Mullard logo. The best quality. Very rare. $39.99 SOLD OUT!

12AT7/ECC81 Brimar UK. Military version. Labeled as CV 4024. Black plate. Excellent quality. Very rare. $29.99 SOLD OUT!

12AT7/ECC81 General Electric USA. In original GE boxes. Very good alternative to Mullard. Well made.$24.95 SOLD OUT!

12AT7/ECC81 RFT East Germany. Precision engineered for great sound. A great price. $19.99 SOLD OUT!

12AU7/ECC82 RCA USA. Black plate. Getting rare. Buy now before they are gone. $23.99 SOLD OUT!

12AU7/ECC82 RCA USA. Grey plate. A very good alternative to the black plate version. $20.95 SOLD OUT!

12AU7/ECC82 Mullard UK. Military version. Labeled as CV 4003. Old style Mullard logo. The best quality. Very rare. $49.99 SOLD OUT!

12AU7/ECC82 RFT East Germany. Manufactured in the former East Germany to exacting standards. A real buy at this price. $29.99 SOLD OUT!

12AU7WA/6189 RTC France. RTC logo in cool green printing. EAMR logo on back in white printing. Excellent sound. Super quality. Very rare. $31.99 SOLD OUT!

12AX7/ECC83 Brimar UK. Military version. Labeled as CV 4004 in original military boxes. Sounds as good as Mullard 12AX7 or Telefunken 12AX7. Very scarce. Almost impossible to find. Buy now before they are gone forever. $34.99 SOLD OUT!

12AX7/ECC83 RFT East Germany. Precision standards at a super price. Sounds as good as Telefunken 12AX7 or Mullard 12AX7. Very scarce and impossible to find now. Buy now before these are gone forever. $69.99 ONLY A FEW LEFT! RARE!

12AX7/ECC83 Mazda Germany. Manufactured by RFT in Germany for Mazda UK. Printed Mazda in very cool blue letters. Sounds as good as Telefunken 12AX7 or Mullard 12AX7. Very scarce and impossible to find now. Buy now before these are gone forever. $69.99 ONLY A FEW LEFT! RARE!

Prices are in US dollars. Availability is limited due to nature of NOS tubes. Shipping and handling costs are extra. Write to me your requirements. I will contact you about payment options(in general bank draft or money order will be accepted), and shipping and handling costs.

I have NOS tubes up for auction on ebay. This is an internet auction site. The URL is Check out what I have for auction. An auction allows the marketplace to bid on items. You can never tell what the final price may end up at - some real good bargains can be obtained by auction. My identification on ebay is : powerlight.

Wanted To Buy

NOS Tubes

I buy NOS tubes - I am particularly looking for Mullard 12AT7/ECC81, Mullard 12AX7/ECC83, Telefunken(<>) 12AT7/ECC81, Telefunken(<>) 12AX7/ECC83, Mullard 5AR4/GZ34, RCA(GT.Britain) 5AR4/GZ34, GE(GT.Britain)5AR4/GZ34, Sylvania(GT.Britain) 5AR4/GZ34, Mullard EL34/6CA7, RCA(GT. Britain) EL34/6CA7, GE(GT. Britain) EL34/6CA7, Sylvania(GT. Britain) EL34/6CA7,Telefunken(<>) EL34/6CA7, General Electric 7199, and RCA 7199. Military versions are acceptable. Send to me your your list with asking prices.

***Attention old radio and television repair shops that are about to close forever.*** Let me know what you have in inventory. You may have the tubes that I want to buy. Once I know what you have, I may be able to make you an offer if you have what I want.

Tube Appraisal Service

I appraise the value of NOS tubes. I will give you a true market value of how much each tube is worth. I have the expertise to identify different varieties of the same tube type by the same manufacturer. Each variety can have a different market value. Plus, I have the expertise to distinguish real tubes from fakes and from rebranded ones. This is very important because there are fakes and rebranded tubes out there. All the tubes I sell are appraised and guaranteed by myself to be genuine. Inquire about the fee structure for this very valuable tube appraisal service. Cost starts at as low as $27.50. Find out how much your tube inventory or tube collection is really worth.

Tube Designations

Vacuum tube designations around the world have always been a source of confusion, primarily because two different systems were developed. Then to add insult to injury, each system had its own military version. So we are now left with four different systems - all describing the same tube type.

To try to clarify this bizarre nomenclature, and make it hopefully easier to identify and collect vacuum tubes, I will attempt to put some order into the chaos.

The two systems consist of 1)the USA one, and 2)the British. Each has its own particular characteristics. Here is one example : 6CA7 is the American designation, whereas EL34 is the British. Both describe the exact same tube, so it is just a question of how you call it. Tubes manufactured in the USA may have printed simply 6CA7 on the glass, or they may have 6CA7/EL34 on it. Conversely, tubes made in the UK may be printed as EL34 or EL34/6CA7. If you have managed to follow along up to this point, congratulations. Now you are ready to get into the military nomenclature - this is were things start to get really scary.

The USA and British military both had vacuum tubes especially constructed for them. The tubes were used in receivers, transmitters, telephones, etc. The military tubes were specified by the army and navy,and built to their standards.

In order to distinguish civilian tubes from military ones, different designations were used. In general the military version was more heavy duty in construction. For example, the military tube may have used thicker mica, or the inside wires were more robust.But,if you examine the internal construction, sometimes the two versions may possibly look identical.

The USA designation for military was JAN which stands for "Joint Army Navy". For example, the military version of 12AX7 is 12AX7 JAN. The British designation was more complex. Each tube was labeled with the code CV which stands for "Civilian Valve" followed by a four digit number. For example,12AX7 has the civilian British designation ECC83.The British military version was called CV 4004. Is this getting complicated, or what? I find the term "Civilian Valve" ironic because the tube was for military purposes - not civilian ones. Could it have been a code to camouflage the idea that it was actually for military use?

Why should you know so much about the military nomenclature? Because the civilian form of NOS tubes is getting depleted for many types, and all that's left is the military version.

Output Tube Bias

Bias of the output tubes in an amplifier is very important both from an operational point of view, and from a longevity point of view. The bias determines the class of operation of a tube amplifier. Of course this depends on the tube type and plate voltage. By varying the bias of a tube, you can shift the operational class(for example, from class B to class A) of an amplifier. This affects the sound of the amp. It also affects output tube life.

Confusion reigns for the term bias as it applies to tube amps and solid state ones. Tube and solid state amplifiers use the term bias in completely opposite ways. Unfortunately, this adds to the confusion in an area which is already misunderstood.

The term bias refers to a negative voltage in tubes, whereas in transistors it is a positive voltage. This is the source of the confusion. Bias voltage controls current flow by applying a voltage across a grid. Negative voltage reduces current flow. Positive voltage increases current flow. So a "high bias" in a tube means high negative voltage applied to the control grid which results in low current flow through the tube from the cathode to the anode. The reverse holds true for "low bias" in tubes.

The problem is in transistor amplifiers the term bias refers to current flow. So "high bias" in transistors means high current flow - the exact opposite of tubes. Hence, when one uses the term bias, it is never clear whether voltage or current is being addressed.

Since transistor amplifiers are more common, the term bias in general refers to current. So "high bias" for tubes can also mean high current if the transistor nomenclature is applied to tubes. Are you following me up to this point? Good. To get high current in tubes, low negative voltage would have to be applied to the control grid. This would actually be called "low bias" using tube terminology.

I would suggest that to avoid confusion, the term bias should universally apply to current as opposed to voltage, no matter what type of amp(tube or transistor) one is referring to. This universal application would be done with the understanding that bias voltage in tubes is the exact opposite in transistors. For example, a tube which is biased low will have a low cathode to plate current, but to achieve this it will be understood that a high negative voltage will be applied to the control grid.

Vacuum Tube Rectification Versus Solid State

The power supply of an amplifier is a critical circuit area because the supply provides both the voltage and current demands of the amp.

Certain musical passages have great dynamic range - especially on compact discs. These passages require a tremendous amount of current. Although this burst of current is required for only a short time corresponding to the brief, but intense, music sections, the power supply must be capable of delivering this current. If it can't, then the music may not have appropriate bass for example.

Some people have gone so far as to say that the power supply determines the musical characteristics of the amplifier.If that is the case, then the type of rectification can be very influential on the overall sound of the amp. Rectifiers provide the DC voltage for the tubes and circuitry. Up until the advent of solid state rectifiers, vacuum tube amps used tube rectifiers.

The rectifier converts AC voltage to DC. The rectifier needs to provide high voltage and high current. A tube amp may typically need 450-500 volts on the plate of the output tubes. At the same time, the output tubes may conduct up to 75-100 mA of current. From this you can calculate how much power the supply must deliver just to one output tube(500 volts X 0.10 amperes = 50 watts). So in a typical push-pull amp with four output tubes, the total power just for the output tubes alone is 4 X 50 watts = 200 watts. That's alot of power for just an amp!

Tube rectifiers are robust in design, and can handle high voltages and current. Tube rectifiers which are very well designed and well manufactured can last a long time. For example, the Mullard GZ34/5AR4 is probably one of the best tube rectifiers ever made. It has been known to last for many years.

The sound of an amp using a tube rectifier is characterized by a phenomenon called sag. At high levels of music the rectifier must supply both high voltage and high current. At high current levels, the tube drops the B+ voltage(typically a drop of 30-50 volts). This results in a lower voltage at the plate of the output tube. Consequently, the volume drops proportionately. Since the high current is only required for a brief moment, the voltage drop is only temporary. Once the current demand returns to more moderate levels, the B+ voltage rises back up to specification, and the volume goes back to its previous level.

The result of all this is a brief drop in volume as perceived by the listener - this drop is called sag. It is brief, and sometimes you have to listen very carefully for it during spirited musical passages. But it is there, and can be demonstrated by simply hooking up a vacuum tube voltmeter (input impedence : 10 megohms)parallel to the output terminals and watching the voltage drop during the peak musical passages.

Vacuum tube rectifiers are slow to respond to power demands in general. This slowness plus sag are partly responsible for the characteristic sound of vacuum tubes.

Solid state rectifiers behave differently than their tube counterparts. No sag is experienced with solid state. As current demand increases, the DC voltage supplied remains constant up to the specifications of the power supply. In addition, solid state rectifiers are quick in response. This gives a solid state amp a faster sound compared to tube rectification.

The million dollar question is which is better, tube rectification or solid state? The classic tube amps had tube rectification, and people got used to the characteristic sound of these amplifiers. Cinemas,rock concerts, and special events all used tube rectified amps until the advent of solid state rectification. Almost all vinyl records were mixed and cut with tube equipment.

But before the million dollar question can be answered, one more technical detail has to be explored. Tube rectifiers provide a slowly increasing DC voltage to the output tube plates as the rectifier warms up. This has an amazing beneficial effect on the output tubes - it minimizes a phenomenon called cathode stripping. This phenomenon occurs with solid state rectification. This is because solid state rectification provides an instantaneous B+ voltage to the plates upon turn on. Unfortunately, this occurs before the output tube has had a chance to warm up. Warm up takes time as the heater increases the temperature of the tube.

The electrons do not start to get emitted from the surface of the cathode until it is warm. In the cold state at start up the electrons are not emitted, but the high B+ voltage is there nonetheless. This results in stripping of the metal film on the cathode surface by the B+ voltage from the solid state rectifier. The ultimate effect of this is that the longevity of the output tube is reduced(by as much as 30%). This does not occur with vacuum tube rectifiers because by the time the slowly rising B+ voltage is present at the plate, the output tube is already itself warmed up.

This is one of the beneficial effects of the vacuum tube rectifiers - increased lifespan of the output tubes. On the otherhand, solid state rectifiers themselves will have a much longer lifespan than their vacuum tube counterparts.

So returning to the million dollar question. In listening tests, I have found that solid state rectified tube amplifiers have certain characteristics of solid state amps - quick response time and more edge. In contrast, tube rectified amps are slower in nature and less sharp in sound. The music from these amps is more round and mellow. Solid state rectified tube amps are agressive in nature whereas tube rectified amplifiers are laid back. In general, I find solid state rectified tube amps to be excellent for rock 'n roll. Tube rectified amps are really good for classical music. Which type of amp you use all depends on your music taste.

My email address is

Last update : November 8, 2009

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