How do tubes work? How is a preamp tube different from a power tube? And what components/elements of preamp/power tubes affect the tone of the amp? (example: what makes EL34’s sound different than 6L6’s, or makes 12ax7’s sound different than ef86’s)
In: Technology
In a vacuum tube there’s a beam of electrons going from one metal piece to another metal piece. That’s why it has to be a vacuum – otherwise the electrons would bump into the air.
There’s a metal mesh or grid in the middle of the beam. When the grid is electrically charged, it pushes electrons away and they don’t want to go near the grid (not even through the holes) which makes the beam weaker.
So you can use it to amplify a signal, e.g. put the beam in between the power supply and the speakers, and connect the grid to the guitar pickup, and now the small amount of electricity from the guitar pickup is controlling the large amount of electricity going to the speakers (it’s actually more complicated than that). So the small variation in electricity, that represents the sound, turns into a big variation in electricity. i.e. a small signal turns into a big signal.
Your amplifier has two stages – the preamp turns the tiny weak signal from the guitar pickup into a medium strength signal, and then the power amplifier turns the medium strength signal into a really strong signal for the speaker. A preamp stage is designed for accuracy because it deals with tiny weak signals; a power amplifier stage is designed for maximum power. If you have a bigger sound system with mixing consoles and stuff, the preamps go at the earliest possible points in the system (i.e. right after the guitars and microphones) and the power amplifiers go at the last possible point (i.e. right before the speakers). Everything in-between uses the medium strength signals.
I’m not an expert on sound, but different tubes may sound different because of different design – basically the same amount of grid charge repels the electron beam a different amount. Especially the “non-linearities” will change the tone of the sound. Adding a bit of charge when the beam is strong probably weakens it more than it does when the beam is really weak, but how much less? You can plot the beam strength vs grid charge on a graph, and different tubes will have different graphs – they’ll be about the same overall shape, but the details can change. Even different tubes of the same type can be different, but the difference is less than with different tube types.
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