To get the most life out of your tubes you should warm them up before playing them. Don't leave the amp on forever because the transformers have a 112 degree F ceiling, and no way to cool down unless the amp is off. As far as longevity of the transformers go, 2 hours on, OFF not standby while you take a break, 2 more hours of on-time. Back to tube longevity. Different tubes have different warm up times. Pre-amp tubes like the 12AX7A take 13 seconds, output tubes take about the same time in most cases. They take longer to warm up as they wear out. So giving them 30 seconds should do. If they play loud and clean when you take the amp off of "standby" then they were ready. Other exceptions are the EL84/6BQ5, and my favorite rectifier the GZ34/5AR4. The EL84 takes about 45 seconds to warm up. The GZ34 takes longer to warm up than any of the other tubes do, and that is by design.

The GZ34 is a slow-start rectifier tube. It's job is to convert the high AC voltage into high DC voltage. Most standby switches disconnect the DC high voltage from whatever rectifier there is in the amp from the other tubes. It would be beneficial to any amp that does not have a standby switch to use a GZ34 rectifier tube. It is pin compatible with the most common rectifier tubes. Any issues would arise if the pin basing were different of if the GZ34 drew more heater current than the other rectfier type. In most cases it's close enough and the power transformer can handle it with out over-heating. The advantage of the GZ34 is mainly that it warms up after the other tubes do, eliminating the need to have or use the standby switch completely. It happens to have just enough compression to please me, greatly.

A lot of Fender amps use a GZ34 at one point in time and then a 5U4 at another. If you use the GZ34 in the amp without a standby switch tubes will last longer because they will not suffer from "cathode stripping." The 5Y3 also has the same pin basing.

Now the biggie no one ever told you about. You need to let your amp cool down for 3 minutes before you move it! A normally functioning tube amp will have bulb temperatures over 300 degrees F. It takes 3 minutes once completely powered down to reach 140 degrees F. Scalding hot is 180 degrees F. The tube is like a light bulb (vacuum, filament), and both undergo changes in shape and in flexibility as they cool. As the filament cools it also becomes more brittle, so if you move the tube as it is transitioning from its' orange hot malleable state to its cold brittle sate you stand a good chance of wrecking the tube. And it not only the heater that behaves this way, but the rest of the electrodes too. The screens get hot too, and I've seen plenty of screen wires get loose in the tube and short out to something else.

So tell your tour manager, the tube amps get switched off first and taken off stage last.

Who makes the best GZ34?

This is for geeks like me. Its misunderstood, there's too much misinformation out there, and my best customers are the ones know something, so here goes. I'll keep it simple, and cover some stuff you wont find elsewhere!

Preamp tubes are in a self adjusting circuit, so they never need biasing. We are referring now to output tubes.

Bias is an adjustment that determines how hot a tube runs. It also determines what the duty cycle is of a tube in a push-pull circuit. The amplifier design determines what class of operation the tube will run in, and so in turn determines what the correct bias point is. Regardless of class, there is a range of proper adjustment!

You need to know what you are doing to make this adjustment or you can seriously damage your
amp, sometimes irreversibly.

Three 'Classes';

Class A: The tube or tubes in the amp each have a 100% duty cycle. That means that the tube is always doing its job of pushing and pulling the speaker. Any amp with only one (output) tube has to be Class A. If there is more than one tube, it can be wired in parallel or in push-pull. Push pull amps can be any class. The parallel configuration is 'single ended', Class A. Most guitar amps 15 Watts and under are Class A. These amps tend to sound very natural, and sustain well.

Class AB: Here amps use tubes in multiples of two. They are arranged 'push-pull'. The duty cycle is 100% at low volumes, and at some point the tubes pass the baton, allowing for operation of each tube more than 50% of the time, and less than 100% of the time. By switching out a tube and allowing it to cool, it is possible to have an output that exceeds the wattage rating of all the tubes added up, i.e.; two 25 Watt EL34's in a 60 Watt amp. Most guitar amps are class AB.

Class B: Also arranged in multiples of two and in push-pull, the duty cycle for each tube is just over 50%, and is never 100% if a signal is applied. These amps use very little current without a signal applied (idle current), and so the tubes may feel relatively cold if on and not being played. 
These amps also employ extremely high voltages, like 700 Volts in a Musicman HD-120. Musicman are the only guitar amps that I'm aware of that use Class B operation. Class B amps tend to sound aggressive.

Since the Audio transformer design dictates Class of operation, how much voltage verses current at idle is also a function of design. Class A runs a lot of current at idle, Class B barely a trickle. Watts equal Amps times Volts, so depending on the design, you may be setting the bias either too hot or too cold when you set the bias to say, minus 52 Volts.

Tubes also vary, and picking an arbitrary bias Voltage can only be useful if all your tubes run at the same potential. Its not the same thing but if it helps, think of it in terms of efficiency. Under any given set of conditions different tubes will perform more or less work. Tubes within a manufactured lot vary. From one model of tube to another of the same type, there is variation. There is an even greater variation from manufacturer to manufacturer.

To build a 6L6 you need to meet the specifications for tube type (beam power, pin basing), for the maximum Wattage rating (ability to deal with heat), maximum plate voltage, maximum control grid to cathode voltage, some inter-electrode capacitance stuff. The point being that there is a lot that's not said about the design. They vary by design and by the fact that they are manufactured (manufacturing tolerances).

I'll bet this is more concise and complete than anything you've seen. I hope you enjoyed it. Feel free to print it for you own personal use but do not duplicate it, as it is copyright protected material.

At this time, Groove Tubes actually does make tubes. They have purchased the original tooling to produce US made 6L6s' and are manufacturing these in the USA. They also make an import KT66 and one particular 12AX7, useing gold in the construction of the control grid. That's all they make at this time. The rest of their tube line is, as it always has been, a representation of all the worthwhile tubes made, mostly currently. They, like Fender, Marshall, Mesa Boogie, Ruby, TNT, do a very good job of screening out the bad tubes and putting their own name on them. To the best of my knowledge, Groove Tubes is the only one on that list who manufactures any tubes, and that represents only a small portion of what they offer. Fender is now shipping "Fender Groove Tubes'" in their amps. All the ones I've seen still carry a third name, the name of the actual manufacturer: Sovtek.

Marshall has dropped Sovtek from certain model amps, and is currently shipping Svetlana tubes in
their amps (pronounced Sevitlana). Prior to that they had used Tesla tubes for a long time, and are currently made also. EI was apparently on the wrong end of Western politics, and the manufacturing plant in Yugoslavia fell down, went boom. Its production of tubes rises and falls to this day. The highly abused Chinese Sino 12AX7 was the tube everyone loved to hate, while at the same time widely used or the production of new amps. The tooling is said to have been put outside, and has gone to rust. I guess another form of friendly fire. 

There is more than one tube manufacturer in China! Lets not lump everyone together unfairly. Just like there is more than one Russian tube company, there are few enough choices in tubes to start getting a National Bias (is this a joking matter?). For anyone who cares, there is a market for American made tubes, as proven by the gentleman who purchased the tooling and licensing of the name from Westinghouse - who is making the 300B in the good old USA. The import 300B's sell for up to $300, so it's a fair guess the American made Westinghouse will cost more. By the way, the 300B is IT for true hi-fi. If you want to buy a guitar amp that uses this 42 watt triode please tell me.



12AX7; the original specification for this family of high-gain dual-triodes. Maximum plate voltage 300V. RCA patented the tube in 1946 and began sales in 1947.

updated specification allows 10% higher plate voltage. This is the current design criteria and relevant tube number. A 12AX7A can be used to replace a 12AX7, but not the other way around. First use about 1954 (ref. GE). 

; this is actually a 12AX7 with an American INDUSTRIAL part number. The 7025 designation indicates additional testing for low microphonics and low hum. Similarly, you would choose one of my Applications Graded TM GAIN tubes, which additionally would be tested for the greatest gain, burned in and listen tested in an actual amp with a specially optimized brutal high gain circuit! If it sounds like an Applications Graded TM GAIN tube is better, it is!

Application Graded TM; There are three different types of circuits in your amp that use 12AX7 tubes. There is the GAIN stage which is the most demanding in terms of sonic qualities, followed by the FUNCTION stage(s) which may or may not increase the gain of the signal but not by much, and then lastly the DRIVER stage which must have each triode within it operating at the same potential in order for you to benefit from those matched output tubes. By sorting the tubes for their best application the amplifier performs far better. Its tone is stronger, the sustain is longer and more natural, and each tube in the amp lasts longer! Hi-Fi tube amps are laid out much like a guitar amp, featuring gain stages and a driver stage. They also stand to gain from properly selected tubes. For other tube based equipment like expensive studio gear and tube foot pedals, a GAIN tube should always be selected.

Burn in; most electronic equipment including tubes will fail within the first 24 hours if it premature failure occurs at all. So to bring out failures, power is applied along with the typical load for a period of time (burn in time).

Clean; the ability of a tube to amplify a signal as designed without adding harmonic overtones.

Compression; In a word, punchy. Compression lessens the dynamic range. The quieter parts of your playing are made to sound louder by making the loudest parts quieter. For example your picking, plucking, swishing and single notes can be made to sound the same volume as a loudly played chord. Or the breath of a singer made to seem as loud as her voice. Technically when the tube runs out of headroom (ability to accept larger input signals while still resulting in proportionally larger output signals) instead of distorting the tube puts out a clean signal but the louder parts don't get represented by as loud of a signal as it otherwise would. If this sounds to you like it gets quieter, then you thinking right, however, the brain interprets the new softer loud part as being a louder soft part. In other words, compression makes the quieter parts of the sound seem louder. For example, a single note could be made to be as loud as a power chord. Tubes compress very naturally, unnoticeably until you learn to listen for it. Compressors deal with rigid predetermined levels for what happens and when - the compression ratio is how much the loud part gets squashed, the threshold is the level that has to be crossed before anything happens. In a tube the compression ratio changes with the amount that you exceed the threshold. In other words, dynamically. Another distinguishing difference is the release time. That's the part That's really hard to get right on a compressor, because it is the time it takes to fade to normalcy. In a tube you never can play in such a way as to hear that gating effect of the release. Tube compressors usually use tubes that are rich, dirty, and ill suited for its use. That's is because the compression brings up all the noise levels. Use a CLEAN COMPRESSED tube in your compressor if you can, to reduce the noise and allow some natural tube compression! Select PRIVATE STOCK for the best possible performance level.

Distortion; tubes either compress or generate harmonic overtones when asked to do more than the tubes' construction allows. In musicians language distortion refers to the latter, rich harmonic texture that is desirable and specific to the way that tubes distort. Technically, any variation in the signal other than amplification is distortion, which compression certainly is, but we do not hear compression as distortion. Instead, we regard the added overtones as obvious and use this definition in music-speak.

Driver; the last tube before the output tubes. In push-pull amps (almost every amp over 15 Watts) the output tubes should have matched performance, although there would be little point if the driver tube was not also matched. More on this and more on the about tubes page.

Dynamic Range; the ability to express yourself in terms of volume. Acoustic guitar for example can play to a maximum volume. That range of volume from the quietest to the loudest is the dynamic range. In electronics, you take into account the noise floor. When measured, this value is expressed in decibels.
ECC83; this is the European part number for the American 12AX7. They are in every way the same tube.

Gain; when the signal voltage comes out at a larger magnitude than it went in then it has gain. For example, the voltage from your guitar swings one tenth of a volt, and the voltage of the same guitar signal after being amplified by the first tube circuit will increase to maybe five volts! Now that is some gain! If the input is the same as the output then it has unity gain. You do have circuits in your amp near unity gain. A tube would really have to be messed up, or you would have to really be rocking the amp for a microphonic tube to be a problem when in a near-unity circuit! 12AT7's are very prone to high frequency microphonics, but due to their pingy tone they only find use in very low gain stages like the reverb driver or the output driver. Different tubes within a batch exhibit differing amounts of gain. The more "healthy" a tube is the more rigid it must be in its construction in order to be usable, ie; a tube may have so much gain that it exhibits an unusable amount of microphonics in a gain stage circuit, and still be perfectly suitable for use anywhere else in the amp.

GAIN/DRIVER; these are a bit hard to come by, and are an ideal choice for experimenters. You can use them as top performing gain stage tubes, or as balanced section Driver tubes equally well. One of these of each tube type make the ideal experimenters kit, as they can each be used anywhere in the amp. Offered at a slight premium.

Headroom; how loud your signal can be before you can expect its behavior to change. What happens when you run out of headroom in a tube is going to be harmonic distortion and or compression.

; when the vibrations caused by amplified sounds cause an internal part of the tube to vibrate in sympathy resulting in a runaway effect similar to sticking a microphone in front of a speaker. All tubes are microphonic to some degree. In preamp tubes the problematic notes always tend towards the higher frequencies. In output tubes the tendency is towards low notes. Since preamp tubes and circuits have more gain, they are more likely to be a practical problem for the player. Most amps are laid out so that the input jack is closest to the tube whose circuit has the most gain. This first tube also imparts the greatest effect on the sound of the amp.

Noise Floor; how loud the noise level is when no signal is present.

; notes in addition to the fundamental one that is a product of the electronics and not necessarily part of the musical source.

PRIVATE STOCK; For a long time I would not sell these to anyone. They are truly the best tubes available of their type. Very few tubes make the grade. When you read about guitar legends who utilize a technician to hand pick the best tubes after listening to hundreds, THIS IS IT. That's what I'm doing, these are the tubes. Offered at an appropriate premium.

Punchiness; a sound quality similar to bassy response but relating to the ability to move a lot of air quickly. Like a punch in the chest.

Re-Amp; a recording technique where the instrumentalist is first recorded without the sound of an amp, then that is played back and recorded through an amplifier.

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