Tube Audio Amplifiers Needn’t Be Complex

There’s a mystique in audiophile circles about tube amplifiers. They can have a very nice sound which is attributed to their even-harmonic distortion, but they are often portrayed as requiring rare and expensive components. You don’t need matched gold-plated tubes and special transformers wound by Japanese monks with oxygen-free silver wire when the tube you’d have found in a TV back in the day paired with a repurposed mains transformer will do. [Mikremk] demonstrates this with a simple but effective amplifier using a PCL82 triode-pentode.

It’s a conventional tube amplifier circuit in which the triode is a preamplifier for the pentode power output stage. The pentode is running in class A mode, and the high impedance of its output is brought down to speaker impedance with that mains transformer. Best of all it doesn’t need a particularly high voltage, with the 40 V DC power coming from a DC-to-DC converter module.

These amplifiers could be found back in the day in some form in most consumer electronics, and remain a spectacularly cheap way to boast a tube amp in your hi-fi even if it might not always be the best possible amp.

25 thoughts on “Tube Audio Amplifiers Needn’t Be Complex

  1. say what you want,but for pure punch,grumble and growl,it takes a big iron core and lots of skinny wire
    talking guitar amplification and pushing pairs of 12″
    tone is in the hands,but an old fender baseman will
    get your attention everytime

    1. No, merely wound transformers lack the essential broader sibilance in the 3-dimensional soundstage, These would transformers are extra-special, a reference technique for the refined aural palate!

      Good spot, editing right away.

  2. Quality tube amplifiers have a unique uncomparable sound.
    I am developing and building quality full tube amplifiers from scratch since many years.
    Remember, there are 2 different thing.
    By one hand you can build with 2 tubes and 3 simple low cost toroidal transformers a stereo amplifier.
    By the other end, to build a hi-fi 2 x 50 w RMS amplifier with a distortion lower than 1 % over the full power range, you need 2 200 VA transformers, one 300VA transformer, 4 power tubes and 12 triodes and 10 additional triodes if you need a RIAA amplifier and adittional Baxandall tone control. I think this explains everything.

  3. It should be noted that the reason guitarists like tube amplifiers is that they _do_ distort the signal, in predictable and controllable ways that have become part of the characteristic sound of a typical electric guitar.

    And that being able to see distortion on a scope, being able to hear it, and finding it with complaining about are very different things. Quoting Mad Magazine many years ago, to the tune of No Business Like Show Business:

    I don’t like to brag how good my speakers are
    But when I turn the sound up real far
    I can hear the dandruff fall from Ringo Starr
    That’s why — I’ve got Hi Fi!

  4. I get a real kick out of “audiophiles” who are willing to spend $300 for AC wall sockets made with oxygen free copper and claim that they can tell the difference in sound. The people who market those things (and other equally ludicrous products) should probably be in jail. I say “probably” because I’m not completely against a tax on ignorance.

    1. Tube amps actually do sound significantly different when overdriven. I’ve been trying to achieve that sound using silicon and/or digital audio processing on and off for years. I think I’ve figured it out, but I haven’t had time to test it. (Supposedly it is because where silicon transistors saturate suddenly, with a hard stop that produces an enormous amount of grungy distortion, tube amps have a compression region before full saturation that allows saturation to happen more smoothly, avoiding the hard grunge you get from silicon. Supposedly germanium diodes can get the tube sound as well, but if you do that, you get overdrive even when the signal isn’t high enough to saturate.)

      So tubes do sound different from transistors, but the difference isn’t a matter of accuracy (as many audiophiles claim). It’s a matter of the quality of the distortion, and it mostly only makes a difference under narrow circumstances. If you want the cleaner, smoother (more common in the early history of electric guitars) sound of tube distortion with your electric guitar, a tube amp is a good choice. If you want the more grungy distortion of a transistor amp, or if you just don’t care and want to save some money, the transistor amp is better. If I was actually good at playing the electric guitar, I would probably want one of each, so I could choose the effect I wanted based on the circumstances. As it is, I’m just working on synth software at this point, so I want both effects to be options. Hard clipping is trivially easy, and I’ve coded it many times. Tube style soft clipping is a lot harder, and I’m still working on tuning the compression region to get the sound I want. I do prefer the soft clipping most of the time, but the grungy stuff does have its place.

  5. it is about taste. I work on the studio side. I produce a vacuum tube mic preamp / optical limiter. In 1997 I could not find what I was looking for in a mic preamp. So I designed one. Then in years later a friend who used to work at Manley Labs talked me into making a Pro Audio version. So I did. My background was that I had worked in recording studios since 1967 and I was a Silicon Valley EE. MOSSWAREPROAUDIO.COM

  6. I posted here, but it must have gotten lost.
    Simple tube amps are simple. They work for some things. If you know all the answers before you start, you just have to get the correct parts and assemble them. This is assuming you don’t care about bandwidth flatness, frequency linearity when changing the volume controls, how long it takes for the VU meter to come in to calibration, achieve the proper bandwidth at the proper flatness. It goes on and on. I design recording studio equipment, rack-mount gear. I worked in recording studios since 1967 as a recording engineer. Multi-track since 1980. I am also a Silicon Valley Engineer and musician. In 1997 when I looked around for the performance I wanted, I couldn’t find it. I had specific needs in the studio. What I designed did exactly what I wanted. Years later I was talked into making a Pro Audio version. I did. It took time to do. This is not HIFI gear. This is recording gear. Take a look.
    Jim Moss

    1. Did you know that the bandwidth for Pro Audio Vacuum Tube Mic Preamps is from 0.5Hz to 55kHz? Lets talk about the 0.5Hz end. Specs are easy to write, but are they true? How would anyone know, the common test equipment typically goes down to 10 to 20 Hz. Well, you have to design test equipment to measure down to 0.5Hz yourself. Do you think the maker of “Simple Tube Amps” will go to that trouble? Someone said a THD+Noise spec of 1%. That is what you might see in power amps of a HIFI system. In the world of Pro Audio Vacuum Tube Mic Preamp the THD+Noise spec is much less and around 0.02%. How does a serious audio engineer get to that low of a THD+Noise spec anyway? There are non-simple design techniques and knowledge. There are also the choice of component materials. Go look around at Pro Audio Vacuum Tube Mic Preamp product specs. Tell me if you can find a 0.2% THD+Noise spec published anywhere. So, the simple tube amp is not what one would like to have in their collection of quality gear, because it does not Mutt The Custard. One more thing, someone mentioned transformers made in Japan. The quality audio transformers are made in California. The materials come from elsewhere, but the winding is done here. So, in the paying recording world simple tube amps are not worth the risk. Just having junk gear in your studio can turn off a potential client. All these things come together to produce a product that costs more than the simple tube amp, sometimes a lot more. In cheap mic preamps they use one triode for the tube effect. That is often used in the output. In Pro Audio Vacuum Tube Mic Preamps the entire audio path is in vacuum tubes. These are not crazy items like the ox free copper either. There are secret sauces for sure, but they are real and understandable. So, if you are OK with your simple vacuum tube amp sounding like a WWII short wave radio, then fine go for it. In Pro Audio studios they need more.

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