What is a tube amp and what do I need to know?

[7 Dying Trees]

There's been a few questions on tube amps lately, and seeing as this quite frankly archaic technology still warms many a musicians heart i thought I'd see if I could knock up a quick guide!

Why tube amplifiers?
well, we don't really know, there's just something magic about them glowing glass tubes. Also something to do with power valves sounding great when cranked as they deliver natural compression, and do nice things to even harmonics. Some people would describe the sound as sweet, singing, you name it. What we do know is that some people prefer solid state, some people prefer valves, this isn't the place to debate it, but overall valves rule the guitar amp world with all boutique amps being valve based, and all the desirable amps being the same (mesa, rivera, soldano, vht, engl, etc etc).

Suffice to say that once guitarists discovered that distorting these tubes produced a musical sound, well, life was never the same again, and solid state amps and modelling amps have been trying to and succeeding to varying degrees, but never nailing it perfectly, to emulate the sound of an overdriven/distorted valve for years. In most electronics the transistor caused the demise of the vacuum tube (even TV's, probably the other last vestige of the tube (cathode ray tube, or electron gun) are now transistor based), but in the music world wherte it is not about efficiency, but rather human hearing, the tube survives.

How do I use the Standby Switch? How Do I turn my amp on and off?
excellent description here:

What is "Standby" for?It was originally a way to cut down some of the wear and tear on the tubes that would otherwise be wearing out while they stood idle. Frequently you'll want to leave an amplifier on but not making any noise, like during a break between sets. The standby switch ensured that the amp would be quiet, and at the same time that the main power supply was disengaged from at least the power output section of the amplifier. This makes tubes last longer.
How should I turn it on?Turn the standby switch on (that is, to the standby position), then turn the power switch on. Wait about 30 seconds (*7DT: Some places recommend 2 minutes, I'd put it somewhere between this, basically, get your amp set up, plugged in, then flip it on standby, do the rest of your set up (pedals etc) and then play, which should easily weat up two minutes, make a cup of tea/coffee if at home and it's already plugged in) and then flip the standby switch to "play". This ensures that the heaters in the tubes are all warmed up and that the startup stresses are as low as possible.How should I turn it off
To turn it off, don't mess with the standby, just turn the power switch off. That cuts both the main power supply and the heater power, so it all simply stops and cools off. The hot tube filaments let the tubes continue sucking current out of the power supply filter caps so the caps are mostly drained of dangerous voltages.

And for you all day players:

Once you've allowed the amp to warm up for at least a few minutes, turn the standby switch to the OFF position and get ready to play! If you find yourself working on music all day long with your tube amp, DON'T continually turn its power on and off throughout the day. Leave the power on and turn the standby on and off depending on whether or not it's in use; you'll save wear and tear on your tubes and likely also find that the amp just keeps sounding better and better (an interesting characteristic of tube amps is that the longer they operate, the better they tend to sound).

Why does my amps impedance need to match the cabinet?
well, basically, that output transformer i was talking about, well, it needs to know what impedance you are running into. Why? well...

If it thinks the impedance is higher than it is, it is thinking it has to work harder than it has to, and pushes the correct amount of power out, but, your load is say 4 instead of 16n ohms that the amp thinks the amplifier is suddenly going to draw 4 times more power than the transformer thinks is going through, and eventually (or pretty soon) the output transformer and or the valves will all fry, taking your amp with it and rewinding transformers is expensive. very expensive. Revalving isn't cheap either, and nor is having to replace burnt fried and cooked components. So don't do it. (I've had this happen due to someone else plugging my amp into a 4ohm cabinet. It fried everything. He paid. He wasn't happy)

The other way around (amp set to 4, cab=16, in other words the amp thinks it's see a lower load than it is) just means it's quieter and will wear down the transformer and shorten valve life (if anything, to be honest this is a gray area, but suffice to say that while not ideal it's not too terrible, and is the only way you can use marshall cabs with mesa power amps, and I have done this and it has been fine. it's not ideal, but should be ok-ish)

Basically for the most efficient power transfer you need to match the amp to the impedance of the cab, or the combined impedance of the cabinets.

In laymans terms:
If you are using one cabinet:
1)Find the ohm rating of the cabinet
2)Set your amplifier to the same ohm rating as the cabinet

If you are using more than one cabinet (ie, a stack)
1)Make sure BOTH cabinets are the same impedance.
2)Take the impedance, and divide it by 2, this gives you tyhe impedance the amp will be seeing, I know it's weird that they don't add up, but that's the way it goes
3)Set your amp to the divided impedance. For instance, if you were using two 16 ohm cabinets, 16/2 = 8, so you set the amp to 8 ohms

Now these days a fair few amps are starting to label the different jacks with what impedance should go into them, which is usefull, but remember, that astill doesn't mean you can plug a 4 ohm and a 16 ohm in (as that would be quite lethal to your amp, especially if you then set it to 16ohms...)

Do I need to attach a load to my amp? What is a load anyway?
well, a load is a name for putting a resistance the amp can see on it. This will almost always be a speaker cabinet, or a power attenuator, or specialised DI device, but 99% of the cases it'll be a good old fashioned box filled with speakers ready to make your poor unsuspecting victims ears bleed. In other cases it would be a dummy load (used when the guy at the amp shop wants to find why your amp isn't working, but wants his ears to live) which would be a specialised resistor that can handle high power (please don't use one from radio shack, in fact, DON'T EVER try and build your own dummy loads unless you really know what you are doing. Unless you have a death wish after listening to my chemical romance, in which case...)

Do you need to attach a load? YES. Even if your amp is idiot-proof as if you don't get into the habit, one day you'll kill someone elses amp, and that's not fair as it will have been through carelessness. So, why is it bad?

Well, you are making the amp see an infinite resistance that it is trying to feed, and all the current it's producing gets stored up and has no way to escape. Think of it this way: You've just drunk 5 gallons of beer, and now you are stuck in a car for 5 hours, can't roll the windows down, and can't get out. Not nice is it?

What is a tube?
A tube (also known as a vacuum tube, electron tube (inside North America), thermionic valve, vacuum tube or valve) is a glass tube with 2 to 5 "plates" inside it and a heating element within a near vacuum (the inside of the tube cntains very little to no air basically (it's not a perfect vacuum).

Anyway... When the heater is turned on (the valves starts glowing) it heats up the cathode. The cathode is made up of a metal that will emit electrons (negatively charged particles). Now, in the simplest form of a tube (a diode) there is only an anode. When the anode is positively charged, it will attract the negative electrons (positive attracts negative) and there will be a flow of electrons from the cathode to the anode, which we know in laymans terms as an eletric current.

Now this isn't very usefull for amplification, we'd like to be able to control this current flow. Hence we can place a control grid in between the two plates (anode and cathode). If we make this plate negative, it will repel electrons, and positive we will attract electrons. By making this plates voltage vary (by feeding a guitar signal into it to look at it simply) we can take a small voltage swing, and prouce a large current out of it and convert that to a larger voltage swing (amplification). Now this isn't exactly how it works (as I forget, it's been a while) but it's the basic principles. A tube with 3 plates is known as a triode. tubes with 4 plates and 5 plates were known as tetrode (beam tetrode etc etc) and pentodes respectively. The reason for having more plates was to try and make the response of the tube more linear within a greater usefull range. To all you people it basically means bleeding more power out of them

You can read more and research if you want to learn more, but basically tubes are finicky devices, there are no equations to describe them (there are too many variables, heater temperature, how perfect or imperfect the vacuum inside the tbe is, distance, and then the effect of the plates, oh, and then try adapting the equation to encompass 3 dimensional field magnetcs and electron flow and all that shit. trust me, it's not nice, otherwise someone would have figured it out by now) and most design is done by pen and paper


What are the differences between tube types?
Right, here's where confusion sets in. basically there arwe a fair few different types of tube. The little ones are mainly preamp tubes and are basically named as model names that the companies produced them used to use that basically describe the properties of the valve. You can look more of this up if you want, but that's for another thread or if someone wants to take the time I can add it in, here's a brief overview in any case:

[FONT=arial, helvetica]1. 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.
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OK, I found a list which should satisfy even the most curious, and it can be found at the bottom of this post -> *(1)
The huge ones that are about the size of light bulbs but with thicker glass and funny thick pins on the bottom are mainly power valves. These can come in triode,tetrode and pentode versions. Basically little ones are for the preamp, big ones for the power amp as a general rule.
Also, in some amplifiers you'll find tube rectifiers, which are basically tube diodes that turn the AC voltage from the mains into a DC voltage for use in the amp.

What are preamp tubes?
The job of these is to provide voltage amplification, or in guitarists case to provide to much amplification to keep the signal clean, thus clipping it and producing what we call distortion. Model names that should be familiar (12ax7,ecc83,ecc81 etc) just describe the valve, but mostly these are dual triodes in one valve. These things can affect the sound a little bit, but mainly in the preamp is the actual circuit that provides the sound. You'll hear people recommending different types for V1,V2 etc in an amp, this basically means that mixing and matching different valve types of different gaisn and roperties produces desirable effects and slightly alters the response of the preamp. V1,V2 here normally correspond to valve positions within the amp. Someone else can elaborate on this

What are power amp tubes?
Power tubes take the output of the preamp section of an amplifier and basically add the "power" to it, and producing a large (very large) voltage swing in the order of about 300-800 volts depending on the amp, design, tube types used etc. Basically enough current and voltage to kill you. Which is why it's not recommended to go tinkering if you don't know what you are doing. Even if it is turned off large capacitances (stored charge) may remain, enough to deliver a shock that will stop your heart, which, could easily be yours with a misplaced screwdriver, voltage meter or slight mishap (and with no mains fuse to blow to save you).

Anyway, power tubes are one of the things that can define the sound of an amp. Models you'll have seen are 6l6, el34, 6550 etc (and others). As a rough guide, el34, think marshall plexi sounds, 6l6 think fender chimey cleans, 6550's think of the modded jcm800's that zakk wylde et all use, were the el34 is replaced by a higher headroom valve (the 6550). For a description of the different sounds, well, someone can write another thread, but this is the general gist.

Why do tubes need to be matched for a power amp?
Power amps normally operate in class A/B (push pull) configuration, where one valve handles the negative swing of the signal, and the other the positive. You'll also hear about class A and B amps etc, but class A/B is the most commonly used. (Mesa's simulclass combines class A with class A/B and require matched quads)...

Anyway, you want the negativer swing to amplify in the same way as the positive swing, hence matched valves. In amps with quads (4 valves) you'll want a matched set of 4 for the same reason.

Anyway, see that huge second transformer? Well, valves don't produces current. Your speakers work by putting a low voltage, high current through them (ie, the signal is an increase/decrease in current, you know, the stuff that kills you, so don't test the output of your amp on your tongue like a 9v battery) so the "output transformer" takes the huge voltage swing, and turns it into a large current swing to drive your speakers.


What is biasing?
biasing is getting the correct base current to flow through the valve. This all has to do with that valves are large physical devices that just are impossible to make the exactly the same over and over again, so there will be differences between thwem.

Note: this says it better:
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Tube bias refers to the idle current of the output tube (power tube). Much like the idle in your car’s engine, a tube amplifier needs to have the output tubes (power tubes) biased properly, for optimal performance. If the output tubes are under biased (idle current is set too HIGH), the audio signal will tend to distort earlier and the tube life will be shortened. This condition is sometimes referred to as biased “too hot”. If the output tubes are over biased (idle current is set too LOW), the audio signal will deteriorate more quickly and the amp will sound thin, cold and sterile. Therefore, this scenario is sometimes referred to as biased “too cold”. Typically, a hotter bias will give you louder, punchier and fuller sound; a colder bias will give you a cleaner, thinner sound.

There is no such thing as the “perfect” bias setting that is acceptable for a particular tube type in a specific amp. There are vast differences in output transformers and tubes, varying quality between tube manufacturers and even significant variation between individual tubes of the same brand and type. Bias ranges are also subject to personal taste. For example, I tend to like my amps biased a bit on the “hot” side, which gives me a more driven sound, but does shorten tube life. Someone else might prefer the sound of a colder bias and longer tube life. Therefore the following table should be used as a guide or starting point. Let your own ears and personal application needs be your final guide.

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Why do people say tube amps are louder than solid state amps?
Good answer to the question below. They are not louder if measured, however, the ear is more sensitive to certain frequencies, and it just happens that, as explained below, tubes just hit those sweet spots in the human ear. (Also has a good explanation as to why a transistor distorting sounds crap, but a valve sounds more musical)

Are Tube Amps louder than solid state amps of the same power?
Yes and no. If you put a power meter on the output of a tube amplifier and a solid state amplifier that have been matched for total output power, then the meter will read almost exactly the same power for equivalent drive conditions - so in this sense, the answer is no, they are not louder. However, if you LISTEN to the two amps, you'll find that the tube amp does indeed sound louder to your ears, in opposition to what the meter is telling you. Why?
It's tied up in the sensing instrument - that is, your ear. The way the human ear works is that it is very sensitive to the harmonic content of a sound. A tube amp is less linear (that is, has more distortion) at signal levels below clipping than a solid state amplifier. The distortion will increase slowly, and then more rapidly as the amp starts to clip. In fact, the distortion increases so gradually and is of such a benign nature that the onset of audible distortion has no easily defined threshold. The solid state amplifier on the other hand has no such gradualism. It is almost perfectly non-distorting right up to the point that it clips, and then it clips HARD. It's easy to hear the threshold.
This sudden onset of distortion is also composed of relatively harsh sounding distortion, not like the subtle second and third harmonics of the tube amp. The human ear hears the sudden harsh distortion as clipping and harshness. It interprets the low order distortion of the tube amp as a louder sound, not as distortion. In effect, the tube amp fools the ear into thinking that its early distortion is more loudness. They therefore sound louder or more powerful than the actual measurements show are really there.

I'll write more if people give me suggestions, but it's an ok start to a huge topic...

Right, for the people that want to read more on the subject as it is huge (thanks to the people that found them!):

Class A - Exposed and Explained by Randall Smith - How a tube amp works - Thanks to JohnnyCNote

euro-e - More tube descriptions, although this is by a guy selling them, so pinch of salt - Thanks to budda



*(1)

[FONT=Impact, Arial, Helvetica]1L6--frequency-converter tube, used in old Zenith Trans-Oceanic radios. Scarce and expensive, this old battery-radio tube tends to wear out quickly. The 1R5 or 1U6 can be substituted by rewiring the socket, with some loss of performance. Out of production, though old stock is occasionally available.[/FONT]
[FONT=Impact, Arial, Helvetica]2A3--power triode, used in single-ended hi-fi amps. Still made in China. Old stock American and European versions are very scarce and expensive.[/FONT]
[FONT=Impact, Arial, Helvetica]2A3 SINGLE-PLATE--original version of this audio triode, made by RCA in 1931 and by a few other firms. Very scarce. Single-plate versions are very difficult to make, a high-cost version is currently being marketed by KR Enterprise.[/FONT]
[FONT=Impact, Arial, Helvetica] 2C39A--UHF power triode, old type--still made by Eimac, and old stock versions are available.[/FONT]
[FONT=Impact, Arial, Helvetica] 3-500Z--power triode used in amateur-radio amplifiers. Popular, but getting expensive. No longer made by Triton ETD (USA) made in China. [/FONT]
[FONT=Impact, Arial, Helvetica] 3C33--power triode--see 6528.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CPX800A7--air-cooled power triode, special pulse-rated version of 3CX800A7. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CPX5000A7--air-cooled power triode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CW5000H3--water-cooled power triode--still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CW40,000H3--water-cooled power triode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX400A7--air-cooled power triode, popular in amateur equipment--see 8874[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX400U7--air-cooled power triode--still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX800A7--air-cooled power triode--popular amateur-radio tube. Still made by Eimac, soon to be made by Svetlana.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX1200A7--air-cooled power triode--Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica]3CX1200D7--air-cooled power triode--Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX1200Z7--air-cooled power triode--Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX1500A7--air-cooled power triode, popular in amateur-radio amplifiers--see 8877[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX3000A1--air-cooled power triode--Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX3000F1--air-cooled power triode--Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX4500F3--air-cooled power triode used in industrial heating--see YU108.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX10,000U7--air-cooled power triode--Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 3CX20,000C7--air-cooled power triode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4-65A--power tetrode used in RF amplifiers. Stll made in China.[/FONT]
[FONT=Impact, Arial, Helvetica] 4-400A--power tetrode used in RF amplifiers. Still made in China.[/FONT]
[FONT=Impact, Arial, Helvetica] 4-1000A--power tetrode used in RF amplifiers. Still made in China. [/FONT]
[FONT=Impact, Arial, Helvetica]4CS250R--conduction-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CV50,000E--large vapor-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CV100,000C--large vapor-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CV250,000B--large vapor-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX300A--air-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX300Y--air-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX350R--power tetrode--Still made by Eimac. Also known as 8930.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX600JB--power tetrode--Still made by Eimac and Svetlana.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX1000A--air-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX1000K--air-cooled power tetrode. See 4CX1000A.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX1500B--air-cooled power tetrode. Still made by Eimac. SED (C Logo) makes 4CX1500A, which is a different type and notplug-in compatible.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX3000A--air-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX20,000D--air-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4CX35,000C--air-cooled power tetrode. Still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 4PR60A--power tetrode used in pulse-power applications. Still made by Triton ETD.[/FONT]
[FONT=Impact, Arial, Helvetica] UX-201A--antique-radio triode, also known as 01A or 301A. Increasingly scarce, not being manufactured, no easy substitute.[/FONT]
[FONT=Impact, Arial, Helvetica] 5AR4--rectifier, widely used in hi-fi and guitar amps. Chinese, Russian and JJ versions available.[/FONT]
[FONT=Impact, Arial, Helvetica] 5R4--rectifier, seen in some old amps. All versions (G, GA, GY etc.) out of production, though old stock is still available.[/FONT]
[FONT=Impact, Arial, Helvetica]5U4--rectifier, seen in some old amps. Still made in Russia.[/FONT]
[FONT=Impact, Arial, Helvetica] 5V4--rectifier, seen in some older hi-fi and guitar amps. Still made in Russia and China.[/FONT]
[FONT=Impact, Arial, Helvetica] 5Y3--rectifier, seen in some older hi-fi and guitar amps. Still made in Russia and China.[/FONT]
[FONT=Impact, Arial, Helvetica] 5Z4--rectifier, seen in old radios. Out of production, though old stock is still available.[/FONT]
[FONT=Impact, Arial, Helvetica] 6A3--power triode, used in single-ended hi-fi amps. Scarce and expensive, out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 6A5--power triode, similar to 6A3. Special type with sleeves over the filaments to decrease hum. See 6A3.[/FONT]
[FONT=Impact, Arial, Helvetica] 6AM6--also called EF91--small RF pentode. Out of production, though old stock is still available.[/FONT]
[FONT=Impact, Arial, Helvetica] 6AN8--small triode-pentode, used in the old Dynaco Mark 3 amplifier and a few others. Out of production, though old stock is still available. A 6GH8, 6U8 or similar can be substituted, by changing the pin connections--suggest contacting an experienced technician.[/FONT]
[FONT=Impact, Arial, Helvetica] 6AQ5--a small power pentode, also called 6005. Often seen in small amplifiers from 1950s. Out of production, though old stock is still available.[/FONT]
[FONT=Impact, Arial, Helvetica] 6AS7--a power triode for power supplies and hi-fi amplifiers. 6AS7 will electrically replace the 6080, which is no longer made. Some equipment does not have room for 6AS7s, as they are physically much larger than 6080s.[/FONT]
[FONT=Impact, Arial, Helvetica] 6BG6--old TV sweep tube, used in some early hi-fi amps. Still made in Russia by Ulyanov. There are many similar sweep tubes, such as the 6CD6 and 6DQ6. Retrofitting equipment to accept the 6BG6 is recommended.[/FONT]
[FONT=Impact, Arial, Helvetica] 6BK4--beam triode used as a high-voltage regulator. Out of production. [/FONT]
[FONT=Impact, Arial, Helvetica] 6BQ5--small power pentode. Also called EL84. Very popular in smaller guitar amps, such as the classic Vox AC-30 which the Beatles used. Also popular in hi-fi. Still made in Russia (2 versions), Serbia and China. SED (C logo) sells the SV83, which is similar to the EL84 except for a lower screen-grid rating of 200 volts.[/FONT]
[FONT=Impact, Arial, Helvetica] 6BM8---triode-pentode, originally for hi-fi and TV use. Still being made by SED (C logo) in Russia.[/FONT]
[FONT=Impact, Arial, Helvetica] 6BQ7--small preamp dual triode used in radio equipment. Out of production, though old stock is still available.[/FONT]
[FONT=Impact, Arial, Helvetica] 6C4--small preamp triode used in early hi-fi equipment. Out of production, though old stock is still available. [/FONT]
[FONT=Impact, Arial, Helvetica]6C19--a small power triode used in high-end amplifiers. Made in Russia by Ulyanov.[/FONT]
[FONT=Impact, Arial, Helvetica] 6C33CB--a big power triode used in high-end amplifiers. Made in Russia by Ulyanov.[/FONT]
[FONT=Impact, Arial, Helvetica] 6CA7--a beam tetrode for guitar amps and hi-fi amps. It is a plug-in replacement for the EL34, but is more rugged. (It sounds quite different from the EL34 and some people prefer the 6CA7.). Suggest having amp modified to accept 6550.[/FONT]
[FONT=Impact, Arial, Helvetica] 6CD6--TV sweep tube. No longer in production. (See 6BG6)[/FONT]
[FONT=Impact, Arial, Helvetica] 6CG7--a medium-power dual triode. Often found in hi-fi amplifiers made by Audio Research. A version is being made by the Ei factory in Serbia.[/FONT]
[FONT=Impact, Arial, Helvetica] 6CL6--small power tube, sometimes seen in older audio equipment. Out of production, old stock is still available.[/FONT]
[FONT=Impact, Arial, Helvetica] 6CW4--Nuvistor tube, used in old FM tuners and some hi-fi and pro audio. Nuvistors are scarce and unlikely to be made in the near future.[/FONT]
[FONT=Impact, Arial, Helvetica]6CW5--small power pentode, also called EL86. Occasionally used in older hi-fi amps and radios. Still made in Serbia by Ei.[/FONT]
[FONT=Impact, Arial, Helvetica] 6DJ8--small preamp tube, widely used in modern hi-fi amps and preamps. Also known as premium types 6922, 7308.A 6922 is still made by JJ in Serbia and in Russia and sold by Sovtek.[/FONT]
[FONT=Impact, Arial, Helvetica] 6DL5--same as EL95. Small power pentode for audio. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 6DN7--TV oscillator tube, used in some hi-fi equipment. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 6DQ6--TV sweep tube--Out of production. (See 6BG6)[/FONT]
[FONT=Impact, Arial, Helvetica] 6E5--Tuning indicator tube or "eye" tube, used in old radios. Old versions are getting scarce. All eye tubes are believed to be out of production at this time. Suggest using a 1629 and adapter available from Antique Electronic Supply.[/FONT]
[FONT=Impact, Arial, Helvetica] 6EA7--see 6EM7.[/FONT]
[FONT=Impact, Arial, Helvetica] 6EJ4--beam triode, high-voltage shunt regulator. Out of production. See 6BK4. [/FONT]
[FONT=Impact, Arial, Helvetica]6EJ7--small pentode, used in Futterman hi-fi amps. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 6EM7--TV oscillator tube, used in some hi-fi equipment. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 6EU7--small preamp dual triode, used in some older guitar amps. One made at the Reflector factory in Russia is available. Also suggest modifying equipment to accept 12AX7 instead, which is very similar.[/FONT]
[FONT=Impact, Arial, Helvetica] 6EY6--beam power tetrode, originally used in TV sets. Out of production. Guitar-amp parts dealers have been marketing this as a replacement for 6V6GT. Sounds different from 6V6GT types, using it is up to the consumer. It will work, but uses much more filament current and will load down the power transformer in a 6V6 guitar amp. (see 6V6GT)[/FONT]
[FONT=Impact, Arial, Helvetica] 6EZ5--beam power tetrode, originally used in TV sets. Out of production. Guitar-amp parts dealers have been marketing this as a replacement for 6V6GT. Sounds different from 6V6GT types, using it is up to the consumer. It will work, but uses much more filament current and will load down the power transformer in a 6V6 guitar amp. (see 6V6GT)[/FONT]
[FONT=Impact, Arial, Helvetica] 6F6--power pentode, widely used in old radios. Out of production. Suggest retrofitting with 6V6GT.[/FONT]
[FONT=Impact, Arial, Helvetica] 6FQ7--version of 6CG7, direct plug-in replacement for it. (see 6CG7)[/FONT]
[FONT=Impact, Arial, Helvetica] 6FS7--medium-power pentode, used in Futterman hi-fi amps. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 6GH8A--small triode-pentode, used in older hi-fi amps and other equipment. Old stock is still easy to find. (Note: there are many plug-in replacements for 6GH8--they include 6U8, 6KD8, 6AU8 and others. Consult a tube manual for more substitutes.)[/FONT]
[FONT=Impact, Arial, Helvetica] 6GL7--see 6EM7.[/FONT]
[FONT=Impact, Arial, Helvetica] 6GM5--version of 7591 with different basing--see 7591.[/FONT]
[FONT=Impact, Arial, Helvetica] 6GW8--power pentode with high-mu triode, also called ECL86. Out of production. 6BM8 made by Svetlana is similar except for pinout, suggest converting amp to accept 6BM8.[/FONT]
[FONT=Impact, Arial, Helvetica] 6HU8--dual pentode, used in old Fisher hi-fi amps. Long out of production. Unique, very scarce and expensive--no easy replacement for it. European number is ELL80. Suggest retrofit to accept 6BQ5/EL84--this requires considerable modification andthe services of an experienced technician.[/FONT]
[FONT=Impact, Arial, Helvetica] 6J5, 6J5GT--preamp triode, used in audio--has underground audiophile following. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 6JK6--small pentode, used in Marantz 10B tuner. Out of production, very scarce. Other types, such as the 6688, may be usable if the equipment is modified.[/FONT]
[FONT=Impact, Arial, Helvetica] 6JE6--see 6JS6.[/FONT]
[FONT=Impact, Arial, Helvetica] 6JS6--large TV "sweep" tube, used in audio, CB and amateur radio amplifiers. Out of production. Scarce and expensive, as are all large American sweep tubes. Suggest modifying the amp to accept SED (C logo) EL509 or EI EL519--requires new socket and rewiring,might require modification to bias circuits.[/FONT]
[FONT=Impact, Arial, Helvetica]6KD6--large TV "sweep" tube, used in audio, CB and amateur radio amplifiers. Out of production. Scarce and expensive, as are all large American sweep tubes. Suggest modifying the amp to accept SED (C logo) EL509 or EI EL519--requires new socket and rewiring, might require modification to bias circuits.[/FONT]
[FONT=Impact, Arial, Helvetica] 6KG6--TV sweep tube--still made in Russia by SED (C logo). (see EL509)[/FONT]
[FONT=Impact, Arial, Helvetica] 6L6GC--beam tetrode, very popular in guitar amps, rarely used in hi-fi. Many versions are still made in Russia, China and Slovakia. Groove Tubes is in production of a GE clone of this tube.[/FONT]
[FONT=Impact, Arial, Helvetica] 6L6WGB--supposed to be a super-premium 6L6GB for military use. Most old American versions were identical to 5881. Current Chinese-made tube under this name is good-quality but physically different from original. Some old-stock American WGBs are available on the surplus market.[/FONT]
[FONT=Impact, Arial, Helvetica] 6LF6--large TV "sweep" tube, used in audio, CB and amateur radio amplifiers. Out of production. Scarce and expensive, as are all large American sweep tubes. Suggest modifying the amp to accept SED (C logo) EL509 or EI EL519--requires new socket and rewiring, might require modification to bias circuits.[/FONT]
[FONT=Impact, Arial, Helvetica] 6N1P--unusual Russian dual triode, similar to a 6BQ7 with larger cathodes and different internal construction. Usable as a plug-in replacement in some 6DJ8/6922 applications. Made in Russia, sold by SED (C logo).[/FONT]
[FONT=Impact, Arial, Helvetica] 6S19P--see 6C19[/FONT]
[FONT=Impact, Arial, Helvetica] 6SJ7--small preamp pentode, octal base. Used in older audio equipment and some modern hi-fi. One made at the Voskhod factory in Kaluga, Russia is available, along with old-stock versions.[/FONT]
[FONT=Impact, Arial, Helvetica] 6SL7GT--small preamp dual triode, high gain, octal base. Used in pre-1956 hi-fis and guitar amps, and in a few modern amps. One made at the Voskhod factory in Kaluga, Russia is available, along with old-stock versions.[/FONT]
[FONT=Impact, Arial, Helvetica] 6SN7GT--small preamp dual triode, medium gain, octal base. Used in older hi-fi and some modern hi-fi. Now made by Sovtek and at the Voskhod factory in Kaluga, Russia, along with old-stock versions.[/FONT]
[FONT=Impact, Arial, Helvetica] 6T5--tuning-eye tube, rare collector's item--can be replaced with 6E5. Out of production. 6T5 has a different glow pattern from 6E5 and other types, making it collectible.[/FONT]
[FONT=Impact, Arial, Helvetica] 6U5--tuning-eye tube, see 6E5.[/FONT]
[FONT=Impact, Arial, Helvetica] 6U8A--triode-pentode--see 6GH8.[/FONT]
[FONT=Impact, Arial, Helvetica] 6V6GT--small beam power tetrode, used in popular guitar amps. A Chinese JJ, and Sovtek versions available.[/FONT]
[FONT=Impact, Arial, Helvetica] 6X4--small rectifier tube, used in older hi-fi. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 10--old power triode, also known as 210 or 801A. It has an underground following with audiophiles. Out of production. It is scarce and getting expensive, demand is very low.[/FONT]
[FONT=Impact, Arial, Helvetica] 12AT7--a common preamp dual triode. Still in production in Yugoslavia by Chinese, Ei, JJ and Sovtek.[/FONT]
[FONT=Impact, Arial, Helvetica] 12AU7--a common preamp dual triode. Still in production in Yugoslavia by Chinese, Ei, JJ and Sovtek.[/FONT]
[FONT=Impact, Arial, Helvetica] 12AX7--the most common audio preamp dual triode. The old Telefunken smooth-plate ECC83 is the most popular style (especially in hi-fi), it is scarce and expensive. Chinese version back in production. Still made in Slovakia (JJ), Serbia (Ei), and Russia (Sovtek). Groove Tubes now offers a Mullard version of the 12AX7 (supposedly made in China).[/FONT]
[FONT=Impact, Arial, Helvetica]12AY7--a special low-noise dual triode for audio equipment. Out of production, old stock is available. GE 6072A is probably the best. There is no other exact replacement, although the 5751 can substitute in some equipment. (see 6072)[/FONT]
[FONT=Impact, Arial, Helvetica]12BH7--a medium-power dual triode, often seen in pro-audio equipment. A version is being made in Serbia at the Ei factory. Old stock is also still available in the surplus market.[/FONT]
[FONT=Impact, Arial, Helvetica] 12BY7--a small pentode used in the Harman-Kardon Citation II amplifier, in Collins transceivers and in old TV equipment. Out of production. Svetlana SV83 MIGHT be usable--considerable (!) modification is required. Suggest talking to a specialist.[/FONT]
[FONT=Impact, Arial, Helvetica] 12DW7--a small dual triode used in a few older guitar and hi-fi amps. A version is made by the Ei factory in Serbia.[/FONT]
[FONT=Impact, Arial, Helvetica] 12X4--see 6X4.[/FONT]
[FONT=Impact, Arial, Helvetica] 13CW4--Nuvistor tube, used as a retrofit in some studio microphones. Out of production. See 6CW4.[/FONT]
[FONT=Impact, Arial, Helvetica] 16BM8--version of 6BM8 with unusual heater voltage--used in Russian series-string TV sets, made in Russia by SED (C logo).[/FONT]
[FONT=Impact, Arial, Helvetica] 20LF6--see 6LF6[/FONT]
[FONT=Impact, Arial, Helvetica] 25E5--small TV sweep tube, sometimes used in Japanese hi-fi receivers of the 1960s. Out of production. Suggest having equipment modified to accept 6L6GCs instead. This is a considerable modification and requires the services of an experienced technician.[/FONT]
[FONT=Impact, Arial, Helvetica] 27LF6--see 6LF6[/FONT]
[FONT=Impact, Arial, Helvetica] 42--power pentode, widely used in old radios. Out of production. Suggest changing socket to allow use of 6V6GT if absolutely necessary--this may decrease the value of a classic radio.[/FONT]
[FONT=Impact, Arial, Helvetica] 45--small power triode, widely used in old radios and sometimes used in single-ended hi-fi amplifiers. Out of production. Old ones are getting scarce. There is no direct replacement; military version VT-52 is even scarcer. (Warning: at least one tube distributor is selling Chinese 2A3s and labeling them as 45s--this will NOT work--the 2A3 requires much more filament power than a 45, and could damage the power transformer.)[/FONT]
[FONT=Impact, Arial, Helvetica] 50--power triode, sometimes seen in old radios and in single-ended hi-fi amplifiers. There is no direct replacement (the 10 is similar but not recommended). Suggest the Cetron 50, which is expensive but is the only one still in production. SE amplifiers can be modified to accept 300Bs by changing the filament supply to 5 volts.[/FONT]
[FONT=Impact, Arial, Helvetica] 80--rectifier tube, widely used in old radios. Out of production. Suggest changing socket to allow use of 5Y3 if absolutely necessary--this may decrease the value of a classic radio. [/FONT]
[FONT=Impact, Arial, Helvetica]83--mercury-vapor rectifier tube, used in old radios and a few early Fender guitar amps. Do not use 5Y3, damage may result. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 101--old audio triode, also called 101A, B, C, etc.... Audiophile cult item, especially in Japan. Out of production, no easy substitute.[/FONT]
[FONT=Impact, Arial, Helvetica] 205--old audio triode, also called 205A, B, C or D. Sometimes called "tennis ball tube". Out of production. Audiophile cult item, especially in Japan. No easy substitute, although Svetlana SV811-3 or SV572-3 could be used by changing sockets and providing 6.3v at 4 amps for filament.[/FONT]
[FONT=Impact, Arial, Helvetica] 210--see 10[/FONT]
[FONT=Impact, Arial, Helvetica] 211--old audio power triode, used in modern single-ended hi-fi amps. Chinese version is inexpensive, some people have qualityissues with it. Old stock is expensive.[/FONT]
[FONT=Impact, Arial, Helvetica] 212E--old audio power triode, also called 212A, B, C or D. Audiophile cult item, especially in Japan. Very large glass tube. Otherwise out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 252A--power triode, audiophile cult item especially in Japan. Out of production. Original version is scarce and sells for $800-up.Suggest using 300B, which is a very similar plug-in replacement. (see 300B)[/FONT]
[FONT=Impact, Arial, Helvetica] 275A--power triode, audiophile cult item especially in Japan. Out of production. Original version is scarce and sells for $250-up.
The 300B may be substituted by adjusting the bias voltage and the plate loading.[/FONT]
[FONT=Impact, Arial, Helvetica] 300A--earlier version of 300B, electrically identical--see 300B[/FONT]
[FONT=Impact, Arial, Helvetica] 300B--power triode, very popular with audiophiles in hi-fi amps. Almost always used in single-ended circuit. Made by Westrex (USA), Richardson/Cetron (USA), China (3 mfrs), Russia (SED C logo) and Reflector/Sovtek), and East Europe (KR Enterprise,AVVT, JJ). [/FONT]
[FONT=Impact, Arial, Helvetica]417A--small preamp triode, very low noise--underground popularity with audiophiles. Out of production, old stock is easy to find.Same as 5842.[/FONT]
[FONT=Impact, Arial, Helvetica] 801A--see 10[/FONT]
[FONT=Impact, Arial, Helvetica] 805--old audio power triode, used in old radio transmitters and some single-ended hi-fi amps. Old stock is expensive, $150 ormore. Still made in China.[/FONT]
[FONT=Impact, Arial, Helvetica] 807--beam power tetrode, often used in older radio equipment and some early hi-fi. Uprated version of 6L6GC with plate cap. Chinese version is being made.[/FONT]
[FONT=Impact, Arial, Helvetica] 809--old audio power triode, used in World War II equipment. Not in production. Suggest retrofitting with 811A or 812A.[/FONT]
[FONT=Impact, Arial, Helvetica] 810--old audio power triode, used in old radio transmitters. Chinese version is inexpensive. Old stock is expensive, $200 or more.[/FONT]
[FONT=Impact, Arial, Helvetica] 812--see 812A[/FONT]
[FONT=Impact, Arial, Helvetica] 812A--old power triode, used in older transmitters and ultrasonic cleaning equipment. Made in China and Russia (Ryazan and SED C logo).[/FONT]
[FONT=Impact, Arial, Helvetica] 813--transmitting beam-power tetrode. Still made in Russia by Ulyanov and in China.[/FONT]
[FONT=Impact, Arial, Helvetica] 829--transmitting beam-power tetrode. Still made in Russia by Ulyanov and in China.[/FONT]
[FONT=Impact, Arial, Helvetica] 832--transmitting beam-power tetrode. Still made in Russia by Ulyanov and in China.[/FONT]
[FONT=Impact, Arial, Helvetica] 845--old audio power triode, used in modern single-ended hi-fi amps. Chinese version is inexpensive, higher-cost Richardson/Cetron version is still being made. Old stock is very expensive.[/FONT]
[FONT=Impact, Arial, Helvetica] 1614--premium version of metal-cased 6L6, originally the standard tube in the McIntosh MC-30 hi-fi amplifier. Scarce, out of production. Suggest using 6L6GC.[/FONT]
[FONT=Impact, Arial, Helvetica] 5687--dual triode computer tube, has an underground audiophile following. Out of production. 6900 and 7044 are plug-in replacements. Used in Audio Note hi-fi equipment. Old stock is easy to find.[/FONT]
[FONT=Impact, Arial, Helvetica] 5691--special rugged version of 6SL7, used in MFA Luminescence hi-fi preamp--very scarce, out of production--see 6SL7.[/FONT]
[FONT=Impact, Arial, Helvetica] 5692--special rugged version of 6SN7, used in underground audiophile equipment--very scarce, out of production--see 6SN7. [/FONT]
[FONT=Impact, Arial, Helvetica]5751--dual triode used in Conrad-Johnson preamps, has a small audiophile following. Out of production, old stock is easy to find. Sovtek now makes one.[/FONT]
[FONT=Impact, Arial, Helvetica] 5763--small beam-power tetrode, used in 1950s radio equipment. Out of production, scarce and expensive. Suggest retrofitting equipment with 6BQ5/EL84.[/FONT]
[FONT=Impact, Arial, Helvetica] 5842--low-noise triode, used in RF and underground audiophile equipment--see 417A.[/FONT]
[FONT=Impact, Arial, Helvetica] 5881--beam power tube, version of 6L6GB--popular in older guitar amps. A version is made in Russia by Reflector/Sovtek.[/FONT]
[FONT=Impact, Arial, Helvetica] 5930--special rugged 2A3--Out of production, scarce and expensive--see 2A3. [/FONT]
[FONT=Impact, Arial, Helvetica]5931--special rugged 5U4--Out of production, scarce and expensive--suggest using Russian 5U4G.[/FONT]
[FONT=Impact, Arial, Helvetica] 5932--special rugged 6L6--Out of production, scarce and expensive--suggest using 6L6GC.[/FONT]
[FONT=Impact, Arial, Helvetica] 5963--special dual triode used in early computers--has underground audiophile following. Out of production, use 12AU7 instead.[/FONT]
[FONT=Impact, Arial, Helvetica] 5965--see 5963.[/FONT]
[FONT=Impact, Arial, Helvetica] 6072A--super-quality version of the 12AY7. See 12AY7.[/FONT]
[FONT=Impact, Arial, Helvetica] 6080--rugged industrial version of 6AS7--physically smaller. Out of production. SED 6AS7 is suggested as substitute, though it may not fit into some equipment made for 6080. (see 6AS7)[/FONT]
[FONT=Impact, Arial, Helvetica] 6094--small beam-power tetrode, used in military equipment--underground audiophile following. Out of production. Old stock is sometimes available.[/FONT]
[FONT=Impact, Arial, Helvetica] 6146--beam power tube, popular in older radio transmitters and found in some audio amps. Chinese version is available from distributors. If quality is an issue, old stock may be available.[/FONT]
[FONT=Impact, Arial, Helvetica] 6201--special high-reliability version of 12AT7--see 12AT7.[/FONT]
[FONT=Impact, Arial, Helvetica] 6267--same as EF86--still made in Russia by SED (C logo).[/FONT]
[FONT=Impact, Arial, Helvetica] 6336--power triode, used in power supplies and some modern hi-fi amplifiers. It was used in an amplifier made by Italian firm Graaf.There is no direct equivalent. Out of production, scarce and expensive. Suggest replacing with 6AS7 if possible--consult with experienced service technician or equipment manufacturer.[/FONT]
[FONT=Impact, Arial, Helvetica] 6360--small power tetrode used in radio equipment. Still made in Russia at Ulyanov factory, under number GU-17.[/FONT]
[FONT=Impact, Arial, Helvetica] 6384--beam-power tetrode, used in military equipment--underground audiophile following. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 6528--power triode, used in power supplies--underground audiophile following. There is no direct equivalent, and it is not in production. Old stock is difficult to find but may be available. Suggest replacing with 6AS7 if possible--consult with experienced service technician or equipment manufacturer.[/FONT]
[FONT=Impact, Arial, Helvetica] 6550--beam tetrode, popular in hi-fi and bass-guitar amps. Original made by Tung-Sol, all American versions out of production. Still made in China and Russia (SED C logo, Sovtek).[/FONT]
[FONT=Impact, Arial, Helvetica] 6550A--slightly uprated version of 6550, 42 watts dissipation instead of 35 watts. Made by GE and Sylvania in 1970s and 1980s. SED C logo SV6550C will work in place of all 6550A types. 6550B, B-2, B-3--older SED 6550 types--obsolete and out of production. See SV6550C.[/FONT]
[FONT=Impact, Arial, Helvetica] 6688--small pentode, low noise, used in radio equipment. Out of production, readily available as old stock. Rarely used by audiophiles in homebrew amps.[/FONT]
[FONT=Impact, Arial, Helvetica] 6696--large water-air-cooled power triode--not in production--suggest retrofit with another type.[/FONT]
[FONT=Impact, Arial, Helvetica] 6697--large air-cooled power triode--not in production--suggest retrofit with another type.[/FONT]
[FONT=Impact, Arial, Helvetica] 6900--super version of 5687--see 5687. Out of production.[/FONT]
[FONT=Impact, Arial, Helvetica] 6922--premium 6DJ8--see 6DJ8 Versions currently made by JJ, Sovtek, and Ei.[/FONT]
[FONT=Impact, Arial, Helvetica] 6973--small beam-power tetrode, originally made by RCA, used rarely in older hi-fi and pro audio equipment. Out of production, scarce and expensive. Sovtek is now producing a 6973 (2005)[/FONT]
[FONT=Impact, Arial, Helvetica] 7025--special low-hum 12AX7--see 12AX7. A Chinese 7025 is being offered by Magic Parts. (2005)[/FONT]
[FONT=Impact, Arial, Helvetica] 7027--beam power tube, similar to 6L6GC. Ampeg used these in guitar amps made in the 1960s and 1970s. JJ now makes a new 7027A. Old versions are scarce. May be substituted by good-quality 6L6GC, or by 6550 if heater power supply is upgraded.[/FONT]
[FONT=Impact, Arial, Helvetica] 7044--dual triode, used in RF equipment and in homebrew hi-fi--see 5687[/FONT]
[FONT=Impact, Arial, Helvetica] 7189--small beam power tetrode, often used in older hi-fi. Out of production. 6BQ5/EL84 is exact plug-in replacement, although older amps apply excessive voltage. If 6BQ5s are used in an amp that specifies 7189s, the plate and screen voltages should be reduced. Consult with an experienced technician. (see 6BQ5)[/FONT]
[FONT=Impact, Arial, Helvetica] 7199--small triode-pentode, used in the old Dynaco Stereo-70 amplifier and many others. A version is made at the Reflector plant in Russia, which is available from audio tube dealers. A 6GH8 or 6U8 type can be substituted, by changing the pin connections--suggest contacting an experienced technician.[/FONT]
[FONT=Impact, Arial, Helvetica] 7241--power triode--see 6528.[/FONT]
[FONT=Impact, Arial, Helvetica] 7242--power triode--see 6528.[/FONT]
[FONT=Impact, Arial, Helvetica] 7247--special high-reliability version of 12DW7--see 12DW7. Currently being made by Ei.[/FONT]
[FONT=Impact, Arial, Helvetica] 7308--premium 6DJ8, guaranteed low noise and low hum--see 6DJ8.[/FONT]
[FONT=Impact, Arial, Helvetica] 7355--small beam power tetrode--used in a few old hi-fi amps. Out of production, scarce and expensive.[/FONT]
[FONT=Impact, Arial, Helvetica] 7408--premium version of 6V6GT--see 6V6GT.[/FONT]
[FONT=Impact, Arial, Helvetica] 7581, 7581A--beam power tube, uprated version of 6L6GC and sometimes given as replacement for KT66. Out of production. Original 7581 made by GE is rare and expensive. It can easily be recognized by its flesh-colored base. There is a 1980s military-surplus version made by Philips/Sylvania which is currently available from distributors.[/FONT]
[FONT=Impact, Arial, Helvetica] 7586--Nuvistor tube, used in some pro-audio equipment--see 6CW4.[/FONT]
[FONT=Impact, Arial, Helvetica] 7591--small beam power tetrode, common in old hi-fi and some guitar amps. 7591 was popular in early 1960s. NOS is getting expensive. Sovtek now makes a direct replacement, the 7591EH. It is about 3/16" larger in diameter than the original 7591A, but works fine. There is no easy substitute, the 7868 and 6GM5 are electrically identical but have different bases--they are also scarce and expensive. Suggest contacting audio tube dealers, if they don't have any then the amp must be converted to 6L6GCs (this is a considerable modification, it will give less output power). Note: JJ is manufacturing the 7591S, which is the same size and diameter of the original 7591A. (2005)[/FONT]
[FONT=Impact, Arial, Helvetica] 7763--beam-deflection modulator tube, often used in early SSB radio equipment. Out of production, scarce. Suggest modifying equipment to accept easier-to-get beam-deflection tubes, such as 6AR8.[/FONT]
[FONT=Impact, Arial, Helvetica] 7788--ultra-high-transconductance pentode, used in RF and audio preamps, has underground audiophile following--see 6688.[/FONT]
[FONT=Impact, Arial, Helvetica] 7868--small beam power tetrode, common in old hi-fi and some guitar amps. Very popular in early 1960s, Sovtek now makes a 7868. (2005)[/FONT]
[FONT=Impact, Arial, Helvetica] 7895--Nuvistor tube, used in Ampex MR-70 tape recorder and other pro-audio equipment. Out of production. See 6CW4.[/FONT]
[FONT=Impact, Arial, Helvetica] 8068--a glass beam power tetrode used in high-voltage power supplies, and sometimes in "homebrew" hi-fi amplifiers. It is a very special tube, capable of operating at up to 3500 volts. Out of production, scarce and expensive. No easy substitute.[/FONT]
[FONT=Impact, Arial, Helvetica]8072--ceramic power tetrode--currently out of production. See 8874. [/FONT]
[FONT=Impact, Arial, Helvetica]8106--small pentode, used in mobile radio equipment. Equipment could be modified to accept 12BY7 or SV83. Suggest talking to an experienced technician.[/FONT]
[FONT=Impact, Arial, Helvetica] 8121--ceramic power tetrode--currently out of production. See 8874.[/FONT]
[FONT=Impact, Arial, Helvetica]8122--matched pair of 8072--ceramic power tetrode--currently out of production. See 8874.[/FONT]
[FONT=Impact, Arial, Helvetica] 8156--small beam pentode, used in mobile radio equipment. Out of production. There is no easy substitute, EL509 or 6BG6 could be used with considerable equipment modification--suggest consulting with an experienced mobile-radio technician.[/FONT]
[FONT=Impact, Arial, Helvetica] 8417--a power beam tetrode used in hi-fi amplifiers. Out of production, scarce and expensive. The Sylvania version was the best, the GE had problems with grid overheating. Suggest having an experienced service tech modify the amp to accept 6550s. This requires rewiring the base and changing the bias circuitry to provide a more negative bias voltage. The amp will produce less power unless the driver stage is extensively modified. Consult an experienced technician.[/FONT]
[FONT=Impact, Arial, Helvetica] 8791V1--TV tetrode, made by Burle.[/FONT]
[FONT=Impact, Arial, Helvetica] 8792V1--TV tetrode, made by Burle.[/FONT]
[FONT=Impact, Arial, Helvetica] 8806--TV tetrode, made by Burle.[/FONT]
[FONT=Impact, Arial, Helvetica] 8807--TV tetrode, made by Burle.[/FONT]
[FONT=Impact, Arial, Helvetica] 8873--conduction-cooled tetrode, popular in amateur radio linear amps (Heathkit SB240)--made by Eimac. Suggest retrofit with different tube, such as SED (C logo) 4CX400A or 4CX800A. The 8874 can also be retrofitted (see 8874).[/FONT]
[FONT=Impact, Arial, Helvetica] 8874--air-cooled triode, popular in amateur radio linear amps--made by Eimac and SED (C logo). Same as 3CX400A7.[/FONT]
[FONT=Impact, Arial, Helvetica] 8875--air-cooled triode, popular in amateur radio linear amps (Dentron MLA2500)--made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 8877--tetrode, popular in amateur-radio amplifiers--made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] 8916--ceramic UHF tetrode used in TV transmitters, made by Burle.[/FONT]
[FONT=Impact, Arial, Helvetica] 8930--see 4CX350R.[/FONT]
[FONT=Impact, Arial, Helvetica] 8950--power tetrode used in mobile radio equipment. Out of production, scarce and expensive. Suggest that the equipment be modified to accept EL509/519, this is an involved job requiring an experienced technician.[/FONT]
[FONT=Impact, Arial, Helvetica] 8975--see 8950[/FONT]
[FONT=Impact, Arial, Helvetica] 8961--see 3CX400U7.[/FONT]
[FONT=Impact, Arial, Helvetica] 8984--ceramic UHF tetrode used in TV transmitters, made by Burle.[/FONT]
[FONT=Impact, Arial, Helvetica] 9007--FM broadcast ceramic tetrode, made by Burle.[/FONT]
[FONT=Impact, Arial, Helvetica] AC701--small preamp triode, used in studio microphones. Out of production, scarce and expensive.[/FONT]
[FONT=Impact, Arial, Helvetica] BW1184--industrial heating triode--still made by EEV.[/FONT]
[FONT=Impact, Arial, Helvetica] BW1185--industrial heating triode--still made by EEV.[/FONT]
[FONT=Impact, Arial, Helvetica] E34L--version of EL34 made by Teslovak in Slovakia--gives slightly more peak power than standard EL34, otherwise similar.[/FONT]
[FONT=Impact, Arial, Helvetica] E88CC--premium 6922--see 6DJ8[/FONT]
[FONT=Impact, Arial, Helvetica]E188CC--super premium 6922 - long life and low noise[/FONT]
[FONT=Impact, Arial, Helvetica]ECC81--European name for 12AT7. (see 12AT7)[/FONT]
[FONT=Impact, Arial, Helvetica] ECC82--European name for 12AU7. (see 12AU7)[/FONT]
[FONT=Impact, Arial, Helvetica] ECC83--European name for 12AX7. (see 12AX7)[/FONT]
[FONT=Impact, Arial, Helvetica] ECC88--European name for 6DJ8. (see 6DJ8)[/FONT]
[FONT=Impact, Arial, Helvetica] ECC803--premium European version of 12AX7. (see 12AX7)[/FONT]
[FONT=Impact, Arial, Helvetica] ECL82--European name for 6BM8--still made in Russia by SED (C logo).[/FONT]
[FONT=Impact, Arial, Helvetica] ECL86--see 6GW8.[/FONT]
[FONT=Impact, Arial, Helvetica] EF86--small audio pentode, low noise--still made in Russia by SED (C logo). Also see 6267.[/FONT]
[FONT=Impact, Arial, Helvetica] EL34--very popular power pentode used in guitar amps and hi-fi. Still made in Russia, Slovakia, Serbia and China.[/FONT]
[FONT=Impact, Arial, Helvetica] EL36--beam power tetrode, TV sweep type, used in some older RF linear amplifiers. Also called 6CM5. No longer in production. Suggest modifying equipment to accept EL509/519. [/FONT]
[FONT=Impact, Arial, Helvetica]EL37--beam power tube, uprated version of 6L6 type. No longer in production. Rare and valuable British tube, has a following among guitarists and audiophiles. Can be replaced with 6L6GC types if rebiasing is performed.[/FONT]
[FONT=Impact, Arial, Helvetica] EL84--see 6BQ5.[/FONT]
[FONT=Impact, Arial, Helvetica] EL84M--Russian-made version of EL84, good quality.[/FONT]
[FONT=Impact, Arial, Helvetica] EL84N--previous name for power pentode now sold by SED (C logo) under name SV83. Has lower screen-grid voltage rating than conventional EL84. (see 6BQ5)[/FONT]
[FONT=Impact, Arial, Helvetica] EL95--see 6DL5 [/FONT]
[FONT=Impact, Arial, Helvetica]EL509--TV sweep tube. Also called 6KG6. One of only two large sweep tubes still being made, 509 is made in Russia by SED (C logo). Serbian Ei version is called EL519, very similar.[/FONT]
[FONT=Impact, Arial, Helvetica] EL519--TV sweep tube--made in Serbia by Ei factory. Plug-in replacement for EL509.[/FONT]
[FONT=Impact, Arial, Helvetica] ELL80--see 6HU8.[/FONT]
[FONT=Impact, Arial, Helvetica] EM1--tuning-indicator tube, European only. Out of production, scarce and expensive. Unique 4-bladed shadow pattern. Used in recent Magnum-Dynalab MD108 FM tuner, as well as old European radios.[/FONT]
[FONT=Impact, Arial, Helvetica] EM80, 81, 84, 85, 87--tuning-eye indicator tubes. Not in production at this time.[/FONT]
[FONT=Impact, Arial, Helvetica] EMM801--Tuning-indicator tube used in the old Dynaco FM-3 tuner. Out of production and getting scarce.[/FONT]
[FONT=Impact, Arial, Helvetica] GI-30--beam power tetrode, made in Russia by Ulyanov. Similar to 5894 and 829.[/FONT]
[FONT=Impact, Arial, Helvetica] GM-70--power triode, made by Ulyanov in Russia. It has an underground audiophile following. Sockets are impossible to find, although an 832-type socket can be drilled out to accept the GM-70.[/FONT]
[FONT=Impact, Arial, Helvetica] GM-100--giant glass audio power triode, made in Russia by Ryazan.[/FONT]
[FONT=Impact, Arial, Helvetica] GS-36B--Russian designator for 4CX400A. Made in Russia by SED (C logo).[/FONT]
[FONT=Impact, Arial, Helvetica] GU-13--see 813. Made in Russia by Ulyanov.[/FONT]
[FONT=Impact, Arial, Helvetica] GU-17--miniature transmitting beam tetrode. Made in Russia by Ulyanov.[/FONT]
[FONT=Impact, Arial, Helvetica] GU-19-1--transmitting beam tetrode. Made in Russia by Ulyanov.[/FONT]
[FONT=Impact, Arial, Helvetica] GU-29--Russian designator for 829A. Made in Russia by Ulyanov.[/FONT]
[FONT=Impact, Arial, Helvetica] GU-32--Russian designator for 832A. Made in Russia by Ulyanov.[/FONT]
[FONT=Impact, Arial, Helvetica]GU-34B--VHF transmitting tetrode. Russian type, manufacturer unknown. Suggest contacting tube dealers in Europe for replacements.[/FONT]
[FONT=Impact, Arial, Helvetica] GU-48--Russian designator for 833A. Made in Ukraine by Poljaron.[/FONT]
[FONT=Impact, Arial, Helvetica] GU-50--VHF transmitting pentode, version of old WWII Telefunken LS50. Made in Russia by Ulyanov, used in a hi-fi amplifier by Manley Laboratories.[/FONT]
[FONT=Impact, Arial, Helvetica] GU-70B--Russian designator for 4CX350A. Made in Russia by SED.[/FONT]
[FONT=Impact, Arial, Helvetica] GU-74B--Russian designator for 4CX800A. Made in Russia by SED.[/FONT]
[FONT=Impact, Arial, Helvetica] GU-91B--Russian designator for 4CX1600B. Made in Russia by SED.[/FONT]
[FONT=Impact, Arial, Helvetica] KT61--beam power tube, similar to 6L6GC. Out of production. Valuable and rare old British tube. May be replaced with 6L6GC. Modification of the amplifier may be required, as the KT61 has higher transconductance and different bias requirements.[/FONT]
[FONT=Impact, Arial, Helvetica] KT63--beam power tube, similar to 6L6GC. Out of production. Valuable and rare old British tube. May be replaced with 6L6GC. Modification of the amplifier may be required, as the KT63 has different bias requirements.[/FONT]
[FONT=Impact, Arial, Helvetica] KT66--beam power tube, uprated replacement for 6L6 types. Was out of production, two different versions were recentlyintroduced by Golden Dragon and Groove Tubes.Valuable old British tube, expensive and scarce. May be replaced with 6L6GC. Modification of the amplifier may be required, as the KT66 has different bias requirements.[/FONT]
[FONT=Impact, Arial, Helvetica] KT77--beam power tube, uprated replacement for EL34. Out of production. Valuable old British tube, expensive and scarce. May be replaced with a top-quality EL34 in some circuits, provided screen-grid ratings of EL34 are observed.[/FONT]
[FONT=Impact, Arial, Helvetica] KT88--beam power tube, similar to uprated 6550. Original MOV/Genalex version is valuable old British tube, expensive and scarce. Still made in China, Russia and Slovakia.[/FONT]
[FONT=Impact, Arial, Helvetica] KT90--beam power tube, used in modern hi-fi amplifiers. Unique KT88-like tube made by Ei factory in Serbia, available from audio-tube dealers.[/FONT]
[FONT=Impact, Arial, Helvetica] KT99--version of KT90--see KT90.[/FONT]
[FONT=Impact, Arial, Helvetica] KT100--Chinese version of KT90, available from Golden Dragon distributors. See KT90.[/FONT]
[FONT=Impact, Arial, Helvetica] M2057--very similar to 8950. See 8950.[/FONT]
[FONT=Impact, Arial, Helvetica] PL519--TV sweep tube with 40-volt heater, made in Serbia by Ei factory. Used in a few high-end amplifiers.[/FONT]
[FONT=Impact, Arial, Helvetica] SV572--audio power triode series, made in Russia, sold by SED. Available in mu of 3, 10, 30, and 160.[/FONT]
[FONT=Impact, Arial, Helvetica] SV811--audio power triode series, made in Russia, sold by SED. Available in mu of 3 or 10.[/FONT]
[FONT=Impact, Arial, Helvetica] TH328--UHF-TV power triode--still made by Thomson.[/FONT]
[FONT=Impact, Arial, Helvetica] TH347--UHF-TV power tetrode--still made by Thomson.[/FONT]
[FONT=Impact, Arial, Helvetica] TH382--UHF-TV power tetrode--still made by Thomson.[/FONT]
[FONT=Impact, Arial, Helvetica] TH563--UHF-TV power tetrode--still made by Thomson.[/FONT]
[FONT=Impact, Arial, Helvetica] TH571--TV power tetrode--still made by Thomson.[/FONT]
[FONT=Impact, Arial, Helvetica] TH582--UHF-TV power tetrode--still made by Thomson.[/FONT]
[FONT=Impact, Arial, Helvetica]VF14--old German radio tube, used in studio microphones. One of the world's scarcest tubes. A new one sells for $1500+. Owners of Neumann U47 microphones are told that only the VF14 is a good-sounding tube in their microphones. U47 owners must buy used tubes from specialist dealers. Suggest consulting an experienced technician.[/FONT]
[FONT=Impact, Arial, Helvetica] Y442--water-cooled tetrode, made by Eimac and SED.[/FONT]
[FONT=Impact, Arial, Helvetica] Y584A--power tetrode (AKA 4CPW10000A0--still made by EIMAC and SED. [/FONT]
[FONT=Impact, Arial, Helvetica]Y644--special version of 4CX250BC--made by Eimac and SED.[/FONT]
[FONT=Impact, Arial, Helvetica] YC108A--power tetrode--made by Eimac and SED.[/FONT]
[FONT=Impact, Arial, Helvetica] YD1202--industrial heating triode----still made by Eimac.[/FONT]
[FONT=Impact, Arial, Helvetica] YU108--air-cooled power triode used in industrial heating, made by Eimac and SED.[/FONT]

 

[nitelightboy]

Lots of good info!!!! Thanks James.

 

[Apophis]

Nice article

 

[7 Dying Trees]

well, i've just added a list of tubes and highlighted the ones guitarists would be possibly interested in red. May have missed some though...

 

[Alpo]

Might just be me, but that red is kinda hard to read.

 

[WarriorOfMetal]

looks good....i agree about the red being hard to read, too.


also, i noticed you didn't put in anything about power-up/power-down procedures for tube amps, which could also be useful info for t00b n00bs

 

[7 Dying Trees]

Might just be me, but that red is kinda hard to read.

Changed it to white

 

[the.godfather]

Some good info there, this is worthy of being 'stickyed' surely?

 

[7 Strings of Hate]

nice james, but like WOM said, it would probably be better to tell the power up and power down procedures, the do's and dont's and things like that. I think most of us tube noobs know that the science of how a vaccum tube works, and thats all we need to know about that part but the tube list did help

 

[7 Dying Trees]

also, i noticed you didn't put in anything about power-up/power-down procedures for tube amps, which could also be useful info for t00b n00bs

Added it in. Interestingly, in another thread, some people were recommending flipping it onto standby and then turning it off. Well, looks like that's the wrong way of doing it as well as the caps don't discharge, and something I never knew properly either! Well, kind of cool, as I am learning stuff by doing this!

 

[WarriorOfMetal]

i sometimes hit a chord on my guitar and then flip the power switch....it helps discharge the caps. then i flip the standby switch to the standby position after the amp goes silent. otherwise i just turn both switches to the off position (in the case of the standby switch, meaning to the silent/standby position) at the same time.

 

[Alpo]

Changed it to white

Mucho better.

 

[7 Dying Trees]

Just added a whole load more, also found a nice description of why tube amps are percieved to be louder, and why the distortion sounds more musical

 

[technomancer]

Sweet Now we need a mod to sticky this biznatch

Oh, double check the end of the section on load matching, as it seems a bit scrambled there.

 

[WarriorOfMetal]

yeah, there are some typos that you might want to go through and fix.

 

[7 Dying Trees]

Sweet Now we need a mod to sticky this biznatch

Oh, double check the end of the section on load matching, as it seems a bit scrambled there.

Well, if someone can do a better description, then post it and I'll edit it in Mine is a bit weird, so please, someone write a better explanation!

THread is meant to collate information into one little guide to read that answers a few basic questions and gives some explanations, so it'd be cool for other people to add in edit and contribute!

And anything else anyone wants to add, or if you see typos, please tell me, as I am not too good at seeing them!

 

[Leon]

i nominate this for Post Of The Year!

 

[The Dark Wolf]

Stickied.


I notice one GLARING typo. Stanby. Missing a D. Might wanna clean up.


Nice post, James.

 

[ibznorange]

lol good work!
there have been more questions on this than usual lately so yeah.
nice bit of info man!

 

[budda]

good thread!

i would have used the tube comparisons from eurotubes instead of that beast of a list (how many of those tubes actually go in guitar amps? condense maybe?) but still a good read.