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Frequently Asked Questions

You may be wondering, what should I know about owning a tube amplifier? Below are some frequently asked questions that may help.

Need help deciding which amplifier is right for you?  Read more here:

How is a tube amplifier different from a solid state amplifier?

Most consumer audio equipment today uses solid state transistors to amplify your source level audio and drive a pair of speakers with sufficient power to desired listening levels. There's nothing wrong with solid state amplifiers; they are efficient and inexpensive and if designed well can be outstanding in quality. In fact, I may offer a few custom made solid state options at some point myself! Many people will choose to buy a solid state amplifier from an electronics retailer or specialty audio supplier and can expect a long-lasting, low-maintenance device that makes their music sound good. Some solid state amps use a switch-mode power supply that uses high frequency pulses of current, helping keep the device physically small. Transistors have very high levels of gain and left uncontrolled would be unusable and would have high amounts of harmonic distortion, so significant negative feedback is used in the circuit design. Solid state amps typically are higher power devices sometimes up to 100 watts per channel or more so they have sufficient power to drive low-efficiency speakers and enough headroom to avoid unpleasant levels of distortion that would occur if the device were underpowered.

Before transistors were invented, vacuum tubes performed the job of amplifying an audio signal. There is a long and rich history of vacuum tubes as high fidelity devices for audio, and many other applications (you can think of all sorts of things: early computers, military equipment, etc.) I describe how tube amplifiers work on my blog, but the short version is that audio tubes rely on high voltage and a heated element to emit and control a flow of electrons inside a vacuum. They are not perfect in their amplification job ("non-linear") which creates natural harmonic distortion, but this is part of their authenticity and signature sound quality. Unlike transistors, this non-linear amplification is not unpleasant sounding at moderate levels. Tube amplifiers, in particular single-ended amplifiers, are lower-power devices so may typically need higher efficiency speakers. But because of the natural amplification sound and nonlinearity curves, you may be surprised to know that it takes only a few watts of power from a tube amplifier to get high quality sound, unlike a transistor that would have undesirable qualities at low power levels.

I see you have different amplifiers. Which one should I choose?

I started Analog Ethos in 2019 by offering just one amplifier, and I have expanded over time to offer several different choices. There are just so many different types of tubes, and combinations of choices about component size or quality, and output power or circuit designs, or physical and visual design!

To help you choose the one that's best for you, use the link near the top of this page to "Help Me Choose."

How often do the tubes need to be replaced?

Tubes do wear out over time. There is a heating element inside that causes a metal cathode to emit electrons that move at high velocity to a metal plate that dissipates even more heat. The vacuum could eventually leak and air molecules inside will collide with electrons enough to make the process no longer work properly. Plus, magical audio spirits in the tubes will whisk away somewhere over time to pursue their eternal destinies. In any case, the tube doesn't last forever if you know what I mean.

This depends on how much time you spend listening to the amp. Remember to always turn it off when not in use, and you'll save lifespan of the tubes. I have had some amplifiers last for many years with the same tubes. And I've accidentally left the amp on overnight quite a few times!

Changing tubes is not like an oil change for your car. You shouldn't feel like, oh wow, it's been a few years, I probably have old tubes that need to be replaced. Keep those guys going as long as you are getting good sound out of them! You'll know if you start hearing noise and hum, lower quality sound, poor volume level or frequency response, the tube no longer heats up and shows the glowing filament, or more obviously if the tube burns out with a sizzle and just doesn't work at all anymore. If the silver "getter" of the tube turns white, the vacuum is lost and this is evidence that air is present and the tube needs to be replaced.

Most of my amps use easy-to-find tubes, not obscure tube models that require you to trade precious gems to faraway merchants. I can point you in a few directions if you need a recommendation on a tube vendor. I usually recommend a reputable dealer, not just anyone selling old tubes on an online auction site.

What kind of speakers do I need?

Most of the amplifiers I'm offering are single-ended designs that use a single tube for each output channel, and these generally have relatively low power output, anywhere from around 3 to 7 watts or so. This means you should have somewhat sensitive speakers if you expect a loud listening volume or have a large room to fill with sound. Speaker sensitivity is measured in dB SPL (sound pressure level). Because of the popularity of solid state amplifiers and the ease and low cost to have high powered output from transistors, many consumer level speakers today are lower in efficiency. A tube amplifier can still work fine with lower sensitivity levels, but I recommend speakers that are at least 90 dB SPL for best performance.

Speakers are one of the most important parts of your sound system, and of course it isn't reasonable to expect good sound from a great amplifier with low quality speakers. Frequency response especially at the low end is difficult to produce without physically large speakers. While I try to have my amplifiers reproduce high quality sound across a typically accepted audible frequency range of 20Hz to 20kHz, most speakers cannot reproduce sound down to 20Hz, and almost no music would ever go that low. If your speakers can do well from around 40-60Hz and up, you should still have a pretty good bass response. Likewise, if you've gone to too many rock concerts or bad marching bands, then your ears may not be able to hear really high frequencies approaching 20 kHz. But again, most music will not be in these extreme values very low and very high.

I design my amps typically for 8 ohm impedance, since this is the most common speaker impedance used for home stereo use. But some of the amps have output transformers that can be wired for other impedance such as 4 ohm speakers. And remember that speaker impedance is labeled nominally, but actually varies significantly over the audible frequency range. It might be 8 ohms at one frequency and 6 or 10 ohms at another, and so on. I have a pair of speakers that are 12 ohms nominal, and use them with an amplifier designed for 8 ohm impedance and it works very well.

Will these amps work with my turntable?

These are all power amplifiers with a volume control. They take a line level input source. To use a turntable, you will need a pre-amplifier with a phono stage. This brings the low level turntable signal up to line level, ready to go to the power amplifier.

Do I need a preamplifier?

You can use a preamplifier if you prefer, but it is not necessary unless you are using a turntable. Then you would need a preamplifier with a phono stage to bring the signal up to line level. If your source level is relatively low, then a preamplifier can help ensure a strong enough signal to drive the amplifier to full output power. If you have multiple sources and would like to switch between them, then a preamplifier is also a useful way to do this.

What kind of input sources are supported?

So far I have chosen to design these as power amplifiers with a single line-level input and a volume control. For people looking for multiple inputs and switching between them, I usually recommend a preamplifier. Everyone has different source needs--some looking for a phono stage, others just line level, and so on. If you just need a few line level inputs and switching, then I would recommend a passive preamplifier as the simplest method. If you have low-level sources or use a turntable, then you would want a powered preamp.

What is "tube rolling" and can I do it with your amps?

Tube rolling is swapping out a different brand or sometimes a different model tube with close enough characteristics that it still works in the amp, but might sound slightly different.

Tubes have a part number that usually includes letters and numbers, such as EL34 or 12AT7. You can use any brand of tube with that same part number. There are a handful of companies producing new tubes today, such as JJ, New Sensor Corp, and a few others. Alternatively, you can buy "new old stock" or NOS tubes, which is a tube made at some point in the past by companies that may no longer be in operation, and the tubes were kept in storage and never used, and are now being sold. Some historically made tubes can be very valuable, depending on the brand, just like anything of high quality vintage nature. You might also find some used vintage tubes that are still in good condition.

Some tubes made with different techniques and having different part numbers can also be substituted for one another because the pin arrangements and characteristics are similar. For example a 6L6GC and EL34 tube can generally be substituted for one another. Others cannot be substituted and could cause damage to the tube or amplifier if used in the wrong circuit. Many tubes use similar sockets, but just because the tube fits, does not mean it can be used!

You can "tube roll" with my amps if you like. How different will the sound be when using different tubes? That depends. Like anything, different manufacturers might use different processes and materials and there is some natural variance in every tube anyway, even from the same brand. No two tubes are perfectly identical. But you generally shouldn't expect it to sound dramatically different. The selection of tube type itself, design of the circuit, and other components like the transformers will shape the performance of the amplifier overall, and rolling tubes is an additional variation on top of those other important elements. I tend to think it's a rather expensive form of experimentation, since a pair of good NOS tubes could easily cost hundreds of dollars, but if it brings you pleasure to try out different tubes, by all means go for it!

What is "bias" and do I have to bias my amplifier?

Bias refers to the steady-state operating point of the tubes at a certain intended level of current. Some amplifiers are designed using a circuit with "fixed bias" which means the voltage difference between the grid and cathode of the tube must be set at a fixed amount so that the right operating point is maintained. As the tubes age or other conditions vary, the amplifier can move away from its normal bias and need adjustment or maintenance.

My amplifiers all use another technique called self-bias, cathode bias, or "automatic bias" where a resistor is used on the cathode of the tube, and if current through the tube ever alters to be higher or lower, the resistor automatically adjusts the voltage on the cathode due to Ohm's Law, bringing the tube back to the expected level of bias. So no maintenance or adjustment for bias is ever needed.

Will a tube amplifier have hum or noise?

Silence when there is no music playing and minimal interference with the program material is of course an ideal condition for any high fidelity stereo system. Many tube amplifiers have some small amount of hum that can be present either from magnetic induction from the power transformer into other parts of the amplifier, or in other ways. Interference from certain poorly-shielded electronic devices placed nearby can also get into the tubes and become audibly noticed.

I design and test my amplifiers to be as silent as possible from hum or other noise. If you place your ear a few inches from the speakers, you may still hear a small hum, but this should not be noticeable from a normal listening position. Certain types of tubes, in particular directly heated triodes such as the 2A3 or 300B, may use alternating current (AC) to power the filament that is also acting as the cathode passing current through the tube. To control hum in my 2A3 amp, I add a potentiometer or "hum pot" which is a variable control to balance the filament voltage so that the hum cancels itself out and the amp can be very quiet.

Finally, there can also be some amount of mechanical noise in a tube amplifier inside the transformer, choke, or tubes given some parts of the design where current is fluctuating at some frequency or a filament is heating up to a high temperature. Again, perhaps audible in close proximity but should not be a concern for listening. All this to say, is a tube amplifier a perfectly silent device? No. But is it a beautiful analog device that makes amazing music nonetheless? Heck yes.

How difficult is it to build the DIY kits?

My DIY kits are intended to be approachable for anyone who is comfortable using small hand tools and a soldering iron. You do not need experience with electronics or ability to read a schematic. My instructions are extremely thorough, with illustrations or photos and step-by-step instructions to take you from start to finish. I also include a very detailed explanation of the circuit and how it works, so you will not only build the amplifier, but will learn how it works (or at least however much you want to learn!)

Some of the components are rather small and require working in little spaces, so some physical dexterity and attention to detail are important! Soldering takes a little practice if you have never done it before, but it is a skill nearly anyone can do. If you are the impatient type who doesn't like to read directions and just wants to plug it in, then buying a fully assembled amplifier might be better for you! But if you have some time and focus, and want the satisfaction of seeing your own work come to life in amazing high fidelity sound, then a DIY kit might be a perfect project.

Won't people think I'm crazy for buying a tube amplifier?

They might, yes. They may say, what's wrong with having the same plain old solid state amplifier that we have? You know, the black plastic one made by robots in a factory somewhere. What do you want with a 2-channel hifi music amplifier when you could have a 5 or 7 channel home theater amplifier and spend your spare time watching Die Hard and Jurassic Park and listening to breaking glass and thundering sound effects on your subwoofer? Who even has a tube amplifier?

Or, maybe they will see it and be curious like you are, and ask you to tell them about it. And you can slip an album out of its cover, click the amplifier on, and show them how an invention nearly a hundred years old can be made by hand in a modern interpretation, can produce incredible and authentic sound, and look beautiful in your home, and you can explain why you love analog.