Hello,

This thread is intended to act as a 'FAQ'. Most common questions can be answered by skimming through the contents of this thread. Use 'Ctrl-F' to search this page for a particular string.
Please don't post here; instead use the search function or start a new thread.

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Tube Basics

The operative parts of a tube are, from inside out, a cathode, control grid(s), and a collector plate. The cathode is always spewing electrons; magnetism on the control grid keeps them in or lets them through.. the plate, charged with a lotta volts, jumps like a spooked cat with each electron that hits. So, when you hook signal up to the control grid, and your output to the plate, you have amplification.

A triode has one control grid, a pentode has three. Each of the three grids does something different, not sure exactly what. All the main power tubes are pentodes, and 12A?7 are twin triodes, two triodes in one glass envelope.

Tubes that have the same pinout -- the same heater pins, plate voltage pin, etc, can generally be swapped out. That makes all the twin triodes - the 12 series (so named because they need a 12v filament voltage when run in series, as they use two 6.3v filaments). AX, AY, AT, AU, they're all swappable with differing gains and whatnot. 12AX7 = max gain, that's why they're so popular for amps.

Here's a run down of what tube alpha-numeric designations "mean", for example a 12AX7
12: filament voltage
AX: model number
7: #of internal elements, including filament

Any extra letters either designate voltage ranges, in which case you want to talk to the distributor is your swapping to find out what exactly you're looking at, or they are design revisions.

Tube amps come in two common flavors, Class A and Class AB.

Class A: The output devices/ stages remain turned on all the time. This reduces thermal variation and eliminates crossover distortion, but is inefficient as you're running full bore across the board all the time, even when you're not pumping your signal through it. Class A amps can be gain monsters or amazing clean machines and are very easy to change tonal characteristics on via tube changes. Massive attack, gobs and gobs of headroom are the territory of Class A amps, not to mention volume beyond what you normally associate with a wattage rating.

Class A/B: The output devices/ stages remain on for only 1/2 of the power cycle (when you have the amp on) and thus more efficiently delivers power as you're only firing on all cylinders when you're playing. The downfall, in my opinion, is that this tends to mello out an amp making it more docile, and the "sweet spot" that is present in Class A/B amps is due to the ramp up of the power cycle as you're playing.

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Common Power Tube Types and Swapping Tubes


EL34, 6550, KT88, KT66, 6L6GC and 6V6 are all the same pinout (called "octal base"). They're swappable to some extent, they have WILDLY differing performance characteristics and major internal adjustment (rebiasing) is needed. In some cases they're fully incompatible. All these tubes use the same socket.

Geek input:

"I just put 2 6CA7EH big bottles in my amp to replace Siemens EL34's and they sound great. They 6CA7EH is a direct replacement for EL34's (with a bias of course). The reason they are different than other EL34/6CA7 tubes is that they are a beam tetrode tube made with the same design as old Philips tubes. The beam tetrode 6CA7 is commonly called the American version of an EL34 due to having the same output, but the American made 6CA7 is tonally of the 6L6 family. It is basically a 6L6 with the high gain output of an EL34. Better Bottom end then regular EL34's, and more durable. I think they are pretty cool, and very cost friendly."

"If you want an alternate to EL34s, one user suggested 6550s. Zakk Wylde uses 6550s in his Marshalls, and with an input boost to push the amp to get a little extra gain, it should sound something like Zakk Wylde... pretty meaty! KT66s also maintain a full range of tones, but are quite expensive. I would go the KT66 route only if you plan on getting most of your gain from the power amp."

"kt-88's are replacements for el-34's, very similar to 6550's, if you have room for their huge bottle design. These suckers are expensive, but worth it if you can afford them. They have a huge bottom end that remains tight without losing any mids or highs. This is truly one the best all around tubes that can go to either end of the spectrum. Billy Corgan used these in his JCM800."

"Thanks for the info on the KT88's! Yeah, that's about what I've heard about them. I read somewhere that it has the low-mid warmth of an EL34 and the mid-high tone of a 6L6. Kinda the best of both worlds I guess."

WARNING: These tubes are not all created equal. Some combinations will explode or melt your amp. Do not swap powertube types without someone experienced in tube-based electronics involved!! This is not something for a novice or even an intermediate to be playing with. This is something for a serious electrical guy, not just a guitar player. Getting it wrong could melt your amp, or kill the guy touching the guitar, and that is absolutely no joke.

The EL84 is a physically smaller tube, the same socket size as 12xx but about twice as tall. They have much lower power (8.5w per tube vs. 30w per tube in an EL34). They are often described as "glassy", which I think of as a sort of sparkly quality to the clean which comes out as a brittle quality when driven. They are definitely not more midrangey than EL34s.

Groove Tubes sells a device called the 'Yellow Jacket' which lets you use EL84 tubes in an octal base amp. One geek had the following review of them: "They are nice. When I was contemplating downsizing my rig and looking at THD's Univalve and Flexi amps I had the chance to swap back and forth a slew of tubes in a Flexi-50, and used the Yellow Jackets for a set of EL84s. Other than the expected change in tone, there was no noticible difference/ noise/ buzz. I was very surprised. The idea that you can re-tube and have in essence a completely different amp is very, very cool."

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12AX7, 12AU7, 12AT7 etc, what's the differences?

These tubes are all interchangeable but have varying gain. The 12AX7s are the highest gain and the most popular vacuum tube on the planet. You can swap all tube types out safely, though it might sound like crap.

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How about that EF86 preamp tube?

EF 86 preamp tubes are described (in several old tube manuals I have read) as being 'hi fidelity', and they were quite a common choice in hi-end audio amplifiers. They were re-introduced to modern guitar amps in the Matchless C-30. Lately I have noticed that the Dr. Z Route 66 uses an EF 86 in it's preamp for the same reason, to supply a very accurate representation of the source sound through to the power amp. I have plugged my guitar into an old tube hi-fi amp (with no less than 7 EF 86's in it's preamp), through to a 2 X 12" speaker cabinet. The tone was the most transparent, lush clean sound I've ever heard, bar none- very little background noise or hiss. When I turned it up, the overdrive was smooth as silk!

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What about Rectifier tubes?

The rectifier converts AC to DC. Some amps do this with a tube -- a 5AR4, 5U4, 5V4, or something like that. Others use a solid state rectifier. Fender and Marshall, notably, use solid state rectification. Mesa and Matchless use tubes. While the prevailing attitude is that tube is essential in the power stage, it is not so clear with the rectifier.

It appears that the actual circuit design decides whether a tube rectifier would make a difference in the tone. Generally this is where "voltage sag" comes from -- once you start actually drawing from your 450v supply, the supply voltage drops. (I find it convenient to think of electricity as water; volts = pressure, amps = flow, watts = units per minute, which is pressure x flow). The 5AR4 will hit a minimum supply of 417v. A 5V4 has a minimum supply of 350 or so volts. Your volume will sag a little bit when this occurs, and naturally "brown out" the sound some. The higher gain your amp is, the crunchier the sound, the more the sag seems to matter.

WeberVST makes "copper cap" replacements for your tube rectifier. Does anyone have any experience with them? They are supposed to sag just like tubes.

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What are these other designations like '7025' and 'ECC83'?

They're different names for tubes that are very similar. For example, ECC83 is the European designation for a 12AX7. This chart should point you towards some common ones:

12AX7 > 7025, ECC83
12AU7 > 5814, 5963, ECC82
12AT7 > ECC81
12AV7 > 5965
EF86 > 6267, CV4004

EL34 > 6CA7
EL84 > 6BQ5
6L6 > 5881
6550 > KT88

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What is NOS? Is it any good?

NOS means "New Old Stock." It's a tube that was constructed in the 50s, 60s etc that has not yet been used. They are usually sturdier tubes, and so they tend to last longer. However, Sylvanias are known for going microphonic pretty quickly.

NOS tubes all sound different... a GE sounds nothing like a Telefunken which sounds nothing like an RCA which sounds nothing like a Mullard. I have some old GE EL84s that I really don't like, but I might if I were playing country. And the nicest power tubes I've ever heard were Telefunken EL84s. I have not heard Mullards except for on Queen's recordings, and we know how great Brian May's tone is.

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What is the glow in the tube? Is that bad?

The glow is usually the heater filament. This heats the cathode so it can emit electrons. It should have *SOME* glow, but can widely vary and it doesn't matter much how bright it is.

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my rig's thread - my playing style

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How should I turn on / turn off my tube amplifier?

Short form: For powering up, turn it 'on', wait one minute, and then take it off 'standby'. For powering it down, turn it 'off', wait at least one minute, and then turn 'standby' on so you don't forget it next time you use the amp.

The standby switch controls the plate voltage. With the switch off, no voltage. If the plates are cold when you hit them with that voltage it seriously affects the metal in ways that greatly shorten the life of the tube. So if you have a standby switch, you should always have it on standby, ie. not "on", when you turn the power on.

However, when turning power off, it's my opinion and practice that you should leave the amp off standby, ie. "on". This has no effect on tube life, but it empties the powerful filter capacitors which store a charge strong enough to KILL YOU if you become its conduit. Leaving standby off for the minute after powering off the amp fully discharges the caps and leaves your amp save to fiddle with.

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Who currently manufactures tubes for guitar amps?

There are five manufacturers: Sovtek and Svetlana in Russia, Shuguang (Sino) in China, EI in Yugoslavia, and JJ/Tesla in the Slovak Republic. JJ/Tesla is so named because this was the Tesla factory, using Tesla tools and based on Tesla and Telefunken designs, but the new company is called JJ Electronic.

Other tube companies, such as Ruby, ARS, Groove Tubes and Electro Harmonix don't manufacture tubes. They buy them in bulk, test them and reject any that don't meet their specs.

One note about Groove Tubes: I believe they have started new manufacture of 6L6GC tubes, but I don't know anything more specific about it than that.

The question was put out to the geeks: What do you think of various tube manufacturers? Here are the responses, by manufacturer:

Sovtek
"Sovteks are usually reliable, sound good and are reasonabley priced."
"I hate Sovteks. They sound like cardboard."
"I will never waste any more money on Sovteks again."
"I've never had an application where the Sovtek tubes improved an amp's tone, in fact I find them to be almost claustrophobic sounding compared to EH or JJ tubes."
"these are my favorites. Smooth transitional breakup, responsive, and what, in my opinion, an EL84 should sound like"
"I wouldn't recommended it for effects users as it has fairly high microphonics, but it does have tone. Easy to break up and crunchy. If you want Sovtek I'd recommend their KT66... a phenomenal all around 6L6 tube."

Svetlana
"Almost all of Svetlana's production goes direct to Marshall. If you get a new Marshall head, it'll have Svetlanas in it."
"Svetlanas are really good, but pricey."
"Svetlana seems to be the best all-around power tube maker, whereas the preamp tubes seem to vary more by preference."

Shuguang
For preamp tubes I use 9th generation Shuguang 12AX7's. They are a a bright sounding preamp tube and go well with the darker JJ's."

EI
"Clean, clean, clean, Very smooth, cheap, but haven't lasted in hotter amps like a Vox."

JJ/Tesla (Note: www.eurotubes.com seems to be a VERY popular JJ supplier with the geeks)
"JJ's are very popular with the members of this forum. I haven't had any experience with them."
"I love JJ/Teslas and NOS tubes."
"I replaced all the original "Mesa" tubes in my Mesa Maverick with JJs (12AX7s and EL84s) and the tone is much much better. It now sounds warmer/darker to me. I hear JJs last longer too, but I don't know that yet...."
"I use JJ 6L6's and can't reccomend them enough. They have a lot of body and warmth to them."
"I use the JJ EL84's in my Koch in combination with 3 JJ ECC83(S) pre-amp tubes for gain and a Sovtek 12ax7wb in the clean channel. (still wondering to switch it out for a ECC83(S) as well, but I wanted as little break up as possible and for that it's a pretty good solution). At shows I often get compliments on how good this amp sounds (no joke) a guy with a Bogner Metropolis asked if I possibly wanted to sell the amp. (thought about it... for about a nanosecond) I'm certainly going to retube my Rivera with JJ's (EL34 or 6L6 or both, haven't decided yet) when I have the money."
"Teslas would also be suitable as they are comparable on gain level and almost as good of a tube but they sound a little darker (than EHX.)"
"I have JJ tubes in my amp and they are badass."
"Low noise, excellent for effects users as it is very balanced, and harmonic characteristics. Very durable."
"Quality, tone, high end tube that in my opinion is worth every penny. Every amp I've used it in has really responded well."

Electro-Harmonix
"I had Electro Harmonix EL34's in the power amp, but one of 'em F***ed out on me."
"I really like the sound of EL34's and the Electro Harmonix tubes sounded good."
"I've have had varying success with EHX."
"I use EHX, but would love to try some NOS tubes."
"For preamp tubes, I like the warm sound of the Electro Harmonix tubes the best..."
"Also may I recommend Electro Harmonix 12AX7s in the preamp... quite warm sounding tubes and I have been ever so happy since I put a EH 12ax7 in the gain stage in my Major. With my Ibanez Jem, it should sound something like Iron Maiden."
"I do believe EH 12AX7s also put out less noise than most 12ax7s on the market at the time being!"
"Electro Harmonix is the only way to go for me. Full, balanced, no noise, their tubes in my opinion allow for my guitar's tone to come through. Beware of re-labeled Sovteks though... unless you prefer the Sovtek sound."
"Dynamic, great smooth power, a good middle of the road priced tube."

Other Resellers
"At the moment in one setup I've got Ruby EL84's in my power amp and Ruby 12AX7's in my Preamp. Sounds good and no complaints."
"My experience with Ruby has been good. I've wanted to try Groove tubes, but they're too pricey for me."
"The Groove Tube 6L6GT (aka GT6L6 GE) are supposed to be amazing...but pricey at like $55'ish each."

NOS
"So far the absolute best sounds for me have come out of NOS tubes."
"Nothing touches an old Telefunken."
"There's a reason that Mullards were the tube of choice for the guitar gods of the '60s and '70s."

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Common Amplifiers and their Tube Complement

Fender Twin Reverb takes one 12AX7, three 7025s (modern equiv: 12AX7) and two 12AT7s.
BassBreaker takes 3 x 12AX7, 2 x 6L6, and a 5AR4 or 5U4GB
Vibrolux Reverb has 4 12AX7, 2 12AT7, and two KT66.

Marshall Studio 15 has 2 12AX7s, 2 6V6
1969 Major has 2 ECC83, 1 ECC82, 4 KT88 (I am running GE 6550s from the early 80s or late 70s sometime as of now... currently no 6550s will handle the voltage for the amp, and few current kt88s will)

Matchless C-30 chassis takes three 12AX7s, a single EF86, and four EL84s. There is also a 5AR4 or 2 5V4 rectifier(s) as well.

Mesa Strategy 500 has 4 6550's, 8 6l6's, and 3 12ax7a's.

Orange AD30TC takes 4 x ECC83, 4 x EL84

Peavey Classic 30 has three 12AX7's in the pre-amp and 4 EL84's in the power amp.

THD's amplifiers (Univalve, Bivalve and Flexi-50) take all sorts of different tubes.

Soldano Astroverb takes 5 12AX7's and 2 EL84s

Vox AC30TBX takes 5 x ECC83, 1 x ECC82, 4 x EL84, and a GZ34 (5AR4) rectifier.
AC30TBR (reverb) 6 ECC83, 1 ECC82, 1 GZ34, and 4 EL84

Ampeg V4/VT22: Four 7027as, 3-12ax7s, a 6k11, a 6gc7, a 12at7 and a 12dw7.

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Biasing a Twin Reverb

(This text was given to me by Bob Pletka @ www.eurotubes.com)

The Twin Reverb is adjustable bias and does not need a resistor change, just a bias adjustment. You can pay someone to do this, or you can do it yourself. Here's how. It's fall down easy to do yourself. All you need is a bias probe. A bias probe looks just like the base of a 6L6 tube, and it fits between your tube socket and your tube goes. Then you turn on the amp, wait 30 seconds, and switch off the standby switch. The probe will read the amount of plate current that the tube is drawing. You only need a single probe because the trim pot controls all the tubes and since your tubes are matched you only need to measure one tube. You can adjust the bias by turning the trim pot which is located on the inside of the amp. To calculate your bias, you should measure the DC plate voltage from pin #3 of any power tube to ground using a multimeter. For most amps it will be between 400 to 500 volts.

The formula for biasing is the plate dissipation of the tube ( 25 watts for a 6L6 or an EL34 ) divided by the plate voltage ( lets use 480 for this example ) times 0.7 will just get you out of crossover distortion and you can go as high as 0.9 (90% of max dissipation).

25 divided by 480 = .0520 or 52 milliamps X .7 = .036 or 36 milliamps

25 divided by 480 = .0520 or 52 milliamps X .9 = .046 or 46 milliamps

25 divided by 500 = .050 or 50 milliamps X .7 = .035 or 35 milliamps so you can see that a variation of 20 volts only equate to 1mA.

A bias probe can be purchased from WeberVST for 90.00 or from Alessandro ( 215-355-6424 ) for 99.99.

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Links

http://www.mclink.it/com/audiomatica/tubes/12ax7.htm
http://www.eurotubes.com
http://www.ibiblio.org/obp/electricC...i/SEMI_13.html
http://www.geofex.com/tubeampfaq/taffram.htm
http://www.tubefreak.com
http://www.aikenamps.com

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Great post!

KT66s are a good EL34 replacement too. They are often categorised with 6L6s, but they are simply a lower wattage KT88 putting them roughtly in the EL34 and 6L6 range (slightly more power handing than a 6L6...). Should get more breakup with KT66s than you would with KT88s in amps around 50 (2) or 100 (4) watts.

With the exception of 5881/6L6 tubes and 6550s and KT88s, most of those tubes are simply different names for the same tube.

5881s actually are 25 watt 6L6s... often they call them 6L6s and sometimes 5881s and sometimes both (6L6/5881)

6550s and KT88s are very close, but KT88s tend to bea bit better made and breakup even more... which is really the only difference...

And with preamp tubes, ECC83, 12AX7 and 7025 are all the same kind of tube, but different names are used in different places and often different applications... for example, in the UK they call them ECC83s, and for home audio they tend to call them 7025s.

You learn somthing new everyday, but after reading all that it wont be about tube amps.

very good, but it just made me want to get my JJ's that much sooner.

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Call me Jem, or Jeremy.

Homophobia is gay.

Attenuation

Fortunately, tube amps sound very, very good. Unfortunately, they sound best when they're cranked up to the max. The neighbors tend to complain. That 100w Marshall isn't all that useful when you can't turn it up past 2 without the sound guy getting in your face. So how do we handle this?

Well, imagine you had two speakers, and one of them was in a soundproof box. You'd essentially be eating half of the power output of the amp, making the thing significantly quieter.

Even better, you could remove the cone from the speaker, and put a knob on it so that you could decide how much power goes to the "dead speaker" and how much goes to the real speaker. Your amp is pushing really hard, but only a little of that sees the speakers. This is the design behind the MASS from WeberVST.

All of the other designs use resistors and inductors in place of an actual moving speaker cone. Some devices require external power, and some don't. (It seems, to me at least, stupid to require electrical power in order to absorb and waste electrical power.)

Common Attenuators:
WeberVST MASS
Weber VST Load Dump
THD Hot Plate
Dr. Z Air Brake
Marshall Power Brake
Scholz Power Soak (amptone.com url)

Extra Info
THD Hotplate vs. Weber MASS shootout

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my rig's thread - my playing style

Simple... kill your neighbors!

I just recently bought a 100 watt tube head. What things are you supposed to do with new tubes? I heard that your supposed to crank up the volume and leave it on all night. Is this true or just somebaody rambling?

thanks

wait a minute, ive always been told that like... you tunr your amp on, wait 2 minutes, take it off standby and play, when you are gonan turn it off, you put teh amp back on standby for liek 2 mintues then turn teh power off... this is wrong?

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Mermaid In A Manhole
www.eyeballrecords.com
Mermaid In A Manhole on Purevolume.com

so then, if you are playing yoru 100W head thru a 4X12 cabinet, what should you do to make it louder? take the cones out or such, im confused at what you are saying

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Mermaid In A Manhole
www.eyeballrecords.com
Mermaid In A Manhole on Purevolume.com

It's not exactly wrong.... here's the only truly important piece: Your amp MUST be on standby for the first minute or two it's on. If you don't, it will damage the tubes. Some amps don't have a standby switch and those usually include some sort of self-warming-up element for an automatic standby.

If you think of electricity as water, you can think of your amp as a complicated water engine, and out the speaker end comes a whole lot of of water. Well, when you turn off this water engine, you shouldn't lock the water into place before doing it. You should shut down and drain the engine.

The same thing is accomplished by leaving the amp off standby when you've cut off the power source. The remaining energy just flows out the speakers, and that's why the sound seems to fade away. You're discharging the powerful and dangerous filter capacitors.

Both Fender and Marshall docs I've seen say that before working on your amp, you should leave the power on, the standby off (ie. in 'run' mode), and the plug unplugged from the wall for 30 minutes.

We're trying to make it quieter, not louder. Do you have a problem not getting enough volume out of a 100w head? That's pretty rare.

If you're running a 100w amp through a 4x12 and it's not loud enough for you, the only thing you can really add is more speaker area -- another 4x12, prolly.

Definitely not that!!! Your amp'll be working hard all night and you'll take a lot of life off your tubes, and also off your output transformer (a very expensive part!). You could cook your OT.

I left the Matchless on overnight once and baked the power tubes. The Match is overbuilt like a mofo and the docs say it can be used, live, continuously (ie. 24/7 indefinitely, not including tube changes.) Those tubes were worthless after that.

I've seen one place that says the first 100 hours of operation changes the tubes' operating characteristics enough to where you might need to rebias the amp, which kind of makes sense as a "breaking-in" period.

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my rig's thread - my playing style

I'm still confuzzled by your explanation of the standby switching on and off

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If Andy Warhol's a genius, then what am I? A speck of lent on the penis of an alien...burried in gelatin.

Argh... I really don't know how to get this across any better than that...


When you start the amp, let it "fill up" for a minute before running it.

When you shut down the amp, "drain" it.

Consider that the "storage" is in between the power switch and the standby switch, so that :

on startup
AC -> powerswitch [on] -> filling up storage -> standby [amp is not running] || nothing.

on shutown

AC -> powerswitch [off] || emptying storage -> standby [amp is running] -> electronics -> sound.

All 'standby' is about is management of that storage voltage. It has to be full to use the amp, and empty to work on the amp. It's nowhere near as important, but on principle I prefer to leave my amp empty when I'm not using it.

Does that make any sense at all?

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my rig's thread - my playing style

actually...yes it does

THANK YOU

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If Andy Warhol's a genius, then what am I? A speck of lent on the penis of an alien...burried in gelatin.