No doubt about it, for the majority of electric guitarists, tube amps sound better. If your with me so far the next logical step is to ask if the tube brands and types are a variable in the tone of a tube amp. Again, from those in the know, a resounding YES! Experimenting with different tubes can be relatively easy and inexpensive way to mess with your amp's tone and learn a lot about how these beasts do the magic they do. First, and most importantly, tube amps contain some VERY HIGH VOLTAGES insde them, enough to KILL YOU! I don't recommend martydom as a nobel deed in pursuit of tone. So when you get started with tube swapping start small - literally. Start with the pre-amp tubes, the smaller tubes found closest to the amps guitar input jacks. In general the larger tubes are the power tubes and if your amp has one, a tube rectifier. This is where you get into some dangerous territory. We'll save talking about power & rectifier tubes for another more in-depth guide, and just focus on the pre-amp tubes for now. Most amps have a tube chart plastered on the inside of the cabinet showing the type and location of the tubes. Those tubes labelled as 12AX7, 12AT7 (any 12Axx), ECC83 (any ECC8x) are preamp tubes and candidates for swapping. The EL84's, 6L6's, 6V6's, EL34's, 5881's, 6550's and KT66's to name a few, are power tubes. The 5AR4's, GZ34's, 5Y3's, typically the tube furthest from the input jack and closest to the power cord, is the rectifier. Preamp tubes serve a number of purposes, amplifying the relatively weak signal from your pickups, shaping tone and changing the gain of the amp. Tone and gain, that's what it's all about and the variations are as broad as the tastes of the players. Typically, the more pre-amp tubes, the more gain stages in the amp. High gain amps with channel switching like a Boogie will have more preamp tubes than a simple amp like an old Fender Champ which has only one preamp tube. When you get started with preamp tube swapping, start easy. There is a wealth on information online about preamp tubes, tube equivilents (same tube, different #) and tube gain, but when you are getting started, just find anothe tube out there with the same number. But all tubes, even the same #, are not created equally. NOS (new old stock) tubes from the bygone eras can be expensive and are highly sought after for good reason. Often made for the military, these tubes are not only durable, but just flat out sound, well, different. I'd be tempted to say better but it's not always so. New production preamp tubes are not expensive, typically less than $15 a tube, so they are a cheap tone tweak. Now, this is where the fun begins. The most influential preamp tube in your amp is likely to be the very first one, closest to the input jack, also known as V1 and is often a 12AX7. This is the tube responsible for kicking up the pickup signal and whatever it does, gets amplified again and again down the chain. subsequent preamp tube slots (V2, V3, etc.) have different purposes and while there are substantial improvements possible by swapping these tubes, the effects can be more subtle. Remember we are talking tone and gain. So get yourself a few 12AX7's, maybe an NOS or ANOS (almost new old stock = used). Play an open G chord and listen to your amp with the stock tube. Listen to the volume, lows, highs,"punch" and clarity of the tone. Now put your amp on standby and swap in another 12AX7. When you pull the first tube, do so by gently wiggling it back and forth while pulling. Note the alinment of the pins and the larger gap in between 2 of the pins. This gap provide your alignment for inserting the new tube. It's a good idea to be able to see the socket and not try to push a new tube in by feel alone. You can bend the pins and make it unuseable. Put in the replacement and let the tube warm up for about 30 seconds. When you take the amp off standby, strum that G chord again. Is it louder? Do you hear a difference in the way certain frequencies are rendered? Is it more or less punchy? Is the tone "warm' or "cold"? Try it again with another tube., and another, and another, and... You'll find that some tubes just work better in V1 of a given amp but don't in others. Some can compliment the tone of one guitar but not another. Regardless, you WILL hear a difference.