What do vacuum tubes do in amplifiers

But there's no sudden point where they suddenly start to clip. Unlike solid state, there would be no sharp edges if you looked at the waveform. So tube amps should sound warmer and more well rounded because of this.

Tubes do go bad, or break. Changing them is pretty easy, however diagnosis of a tube problem can be a little bit harder. You may be replacing a stock tube for an upgrade, or replacing an old one which may have developed a fault similar to below.

The most important thing to keep in mind is that you need to replace like for like. Preamp tubes don't usually need rebiasing, however once you've settled on a new pair of power tubes a rebias may be needed. Even tubes of the same brand aren't always going to be the same, especially when they're from different batches. Your amp may run fine without a rebias - but I'd certainly recommend you get it done.

One of the problems with tubes is their inconsistency - an ideal bias will be different in identical models. The most you should do, even to an unplugged amp, is change the tubes. If you have any doubts about anything consult an amp tech. This information should serve as general advice only and act to narrow down potential issues. Amp are complex so what you think is an obvious solution may not be the case. Many of the problems listed below can can be confirmed simply be placing an old set of tubes you know work into your amp.

For the more serious problems below amp not turning on they can still be a useful tool in helping your diagnosis. This is one of the least serious, and perfectly normal signs. If your tubes have had a good run several years they usually last depending on use then they may just be past their best and need replacing.

There may be nothing wrong with them from a technical point of view, but if it drops below what you think is an acceptable level, then a change is needed.

The old tubes are good to keep as a test pair for diagnosing potential future problems. If your tubes have been in for a while it may be time to change them. Generally, power tubes wear out faster than preamp tubes — so look at them first.

If you want to be a nerd about it, try to keep a note of the approximate age of a tube. This will help you narrow down the problem tube. In a way this is similar to above. Your amp may be quieter than it once was. Look below for visual signs that a tube has failed. This one may be straightforward.

The problem is usually a connection breaking somewhere in the tube. Read below for identifying the bad tube or try one of your old stock tubes in each position until you find the culprit.

Your amp could be working fine but then have a sudden drop in volume, or even turn off completely. This may be the first sign of a tube slowly giving up. However, it could also be the sign of something else. Try testing with an old stock tube and see if that solves the problem.

The first thing you should do is check the fuse. These exist for safety reasons and to protect your amp. If too much current flows through the device the wire in the fuse melts and breaks the circuit. If they have both blown then it could indicate a problem with your amp. It may be an idea to get an amp tech to look at your amp. If you find that is is just one tube, then replacing the fuse and blown tube could sort your problem easily.

So you think a tube may be bad, but how do you know for sure? And which tube is it? After reading how a tube works above, it becomes obvious why. But if you replace with another tube, and it starts to glow, you can be pretty certain it was the tube. This one is an easy diagnosis. Red plating is when the plate in addition to the filament glows red and looks kind of sinister. An amplifier without natural harmonic distortion sounds unnatural, however, so some modern amps called modeling amps tend to mimic the sound of tube amps.

On paper, it would seem that solid-state amps beat tube amps squarely. However, the warm and mellow sound produced by tubes makes them worth all the extra expense and effort required to use them. Tubes require regular checking and swapping depending on the frequency of playing. That could be anything from 6-month intervals to a couple of years. Vacuum tubes wear out naturally with time. They can simply burn out, or gas can form inside the tube and make them less effective.

This causes them to become less effective. Here are some signs of bad tubes. When you have a faulty valve, it is advisable to replace all of them at once. This ensures correct biasing and restores full performance. You should always have replacement valves with you in case of failure because sometimes playing with a bad one can damage the other internal components. This should be a problem, however. They are designed to resist feedback and make a lively upgrade to your old tube amp, and are some of the most popular 12AX7 preamp tubes out there.

Once you have determined that you have a bad vacuum tube, the next step is to remove and replace your tubes following the recommended safety guidelines. Yes, most manufacturers account for this in their design. The vacuum tubes in a tube amp generally last 5, to 10, hours of play time.

However, this depends on the intensity of use. Yes, tube amps certainly sound better than solid-state amps and any other alternative technology. Even without being a purist, you will hear the difference in the warmth and character of the sound they make compared to the cold, clean sound of solid-state amps.

Vacuum tubes wear out with use, so it is better to always turn off your amp when you are done using it. They also tend to overheat and use up a lot of power, so it is safer and cheaper to have them off until they are needed.

If you just need an amp for practice or move around a lot, a tube amp is not worth the money or effort required. You might want to check out our top five bass practice amps for this instead.

Yes, tube amps need about minutes to warm up properly before you can start playing on them. Your manufacturer will have provided guidelines on this. This will give you maximum character even at relatively lower volumes. It is always advisable to buy high-quality tube amps from recognized manufacturers in the first place, such as Fender or Marshalls.

Century-old technology still trumps the most advanced transistor and microchip technology when it comes to amplifying guitar music. The natural harmonic distortion that tube amplifiers produce is what makes them worth all the effort required in maintaining and using them. Hopefully, now you understand how tube amps work from this simplified explanation.

The amps themselves are so simple that you can build one yourself given the right parts, but the technology behind them is simply ingenious. You can also now take better care of your old tube amp, and perhaps even perform a few minor upgrades to get the best sound.

Remember to enjoy the mellow sound of these antiquated units before impostor technology sweeps them all to the graveyard. Your email address will not be published. Home » Gear » Amplifiers. A detailed guide on how vacuum tube technology works, components and schematic of the tube amps, and useful tips on how to replace a bad tube. By Alecia Steen Alecia Steen. Active 4 years, 7 months ago.

Viewed 60k times. Aditya Gupta Aditya Gupta 55 1 1 gold badge 1 1 silver badge 3 3 bronze badges. Also, what diagram are you referring to?

What have you done so far? Have you tried googling for answers? What clarifications do you need? People will be more inclined to answer your question if you have shown research effort. Instead ask a new question, although it might be worth adding some details on the parts you don't understand. Add a comment. Active Oldest Votes. Please post that link. Otherwise it is plagiarism. Which is wrong. But per your suggestion, I added links above each of the pictures to the articles where they came from.

And your assertion is evidence-free. Show 1 more comment. These are the basics. For more, the electrical engineering site would be more appropriate. Alfred Centauri Alfred Centauri Since a capacitor will block DC but allow AC to freely pass through, the bypass cap does what its name implies—it allows the electrons needed for amplifying the guitar signal to bypass the resistor and flow freely through the cathode. Larger values would let more bass through, while smaller values would reduce it.

Signal capacitors, meanwhile, are the small caps inside the amp, and they perform two critical functions. First, they block DC voltage while allowing AC voltages like the guitar signal to pass through. They also determine, according to their value, which guitar frequencies will pass through.

In other words, signal caps define the tone of the amp. AC4 signal-cap values range from. Smaller values like the. Put another way, the tone control sends high frequencies to ground instead of letting them reach the power tube. These are the small, cylindrical components with color-coded stripes indicating their value.

If you haven't already guessed by their name, they resist the flow of electricity. They are represented in the schematic as a peaks-and-valleys shape, like a seismograph reading or a few capital V's strung together.

Higher values resist the flow more than lower values. In doing so, they decrease voltage as electrons try to travel through. A "k" after a number indicates thousands i. In addition to ohms, resistors have a wattage rating. Wattage needs to be higher if the resistor is in the power section. Note: some amps will use a component called a "choke" here rather than a resistor.

A choke is an inductor that looks like a small transformer. Inductors don't like changes in current flow, which means they will help choke out some of the ripple we spoke about, reducing amp hum. The first tube that your guitar pickups' signal will get to is the first preamp tube.

Remember the three elements inside a tube—the cathode, plate, and grid? The presence of those three elements define the tube as a triode tube. An EF86 adds two more elements, making it a pentode from the Greek term "penta," meaning "five".

The two additional elements within a pentode are the screen and the suppressor. Like the grid, the screen and suppressor are wire wraps inside the tube, not continuous metal. This allows them to impose charges that affect the electrons while still allowing the majority of electrons to pass through. The presence of the cathode and plate within the tube makes the tube itself something of a capacitor.

To reduce that unwanted capacitance, the screen is placed between the cathode and the plate, with a DC voltage applied. The suppressor is the wire wrap closest to the plate, and it is connected to the cathode. In an EL84, this connection is made within the base of the tube. Because the suppressor has large gaps in it, it has virtually no effect on electron flow from the cathode.

Still, some electrons will hit the plate and bounce off. The suppressor sends the electrons from these "secondary emissions" back to the plate. Just as the guitar signal is amplified by the preamp tube, the signal from the preamp tube is amplified by the power tube.

In an AC4, it's an EL The five elements in this pentode tube perform the same functions as the triode EF86's elements, only with greater current passing through. Looking at the schematic, you'll notice something different about the 12AX7 relative to the EF It's a dual triode, meaning it has two separate triodes in a single tube.

As used in the AC4 vibrato circuit, the two halves work closely together. Unlike some other amps' tremolo circuits, which let you control the speed and intensity of the effect, the AC4's only offers a knob to govern speed. When the AC4's footswitch is open i. It sends a voltage to the cathode of the EF86 preamp tube in pulses, while an array of capacitors and resistors along with the speed control determine the rate.

Closing the footswitch sends the oscillation to ground, deactivating the vibrato effect. The two halves of the 12AX7 are wired to invert the AC sine wave. Electron flow in the two halves works degrees apart— completely opposite. There are three signal capacitors in the vibrato circuit, and each one offsets the sine wave 60 degrees. The vibrato speed control affects that offset. As mentioned, think of the vibrato circuit as outputting a low-frequency oscillation, 2—10 cycles per second—too low to hear as a sound, but affecting the EF86's cathode bias that many times a second.

If you look at the schematic, you'll see that the oscillation originates on the right side of the 12AX7, sending it to the grid on the left side. The cathode pin 3 sends the oscillating voltage to the EF The result is a variation in the preamp tube's ability to allow electrons to flow, 2 to10 times per second.

It may seem strange, but an amp's output transformer doesn't just provide power in any old way— it's critical to shaping the amp's sound. It does something interesting. Electrons flow through the power tubes' plates at high voltages but low current. The output transformer converts that to a low-voltage, highcurrent signal that will drive the speaker. The high DC voltage on the tube side of the output transformer will not pass to the speaker side—the output transformer blocks DC. But it will transfer the AC guitar signal to the speaker side.

Output transformers are rated in impedance i. The AC4's 8"speaker is rated at 3. A single EL84 puts out 4 to 5 watts, so the speaker needs to be able to handle that it shouldn't be a problem for most speakers—that wattage is pretty low.

The ground connection plays a big role in understanding the flow of electrons through the power tube and to the output transformer. This simplified schematic shows the basic circuit. The amplified guitar signal pulls electrons from ground, through the bypass capacitor to the EL84 tube, through the output transformer, and through the filter capacitor back to ground. The designation of "class A" is often a topic of hot debate for some tube-amp enthusiasts.

A guitar amp can run its tubes in class A, class AB, or class B. Other classes exist, but not for audio applications. Class A describes an amp in which a power tube conducts the entire sine wave of the guitar signal.