Buying an amplifier is one of the most important choices for any guitarist. Why? Because the right amp can make your guitar sound great and the wrong amp can make it sound like well, you get the drift. Your first task is to think about what your needs are as a musician. If you're just going to be playing alone at home, your needs will be very different from a guitarist who plays club dates, or from the pro who works in studios or at large concert gigs. Let's look at the wide world of amps and see what's the right amp for you.
Tube vs. Solid State
This is the debate that's lasted 30 years. In a nutshell, tubes represent the vintage technology that powered all electronics during the middle of the 20th century. They deliver great tone in many guitar amps, but require periodic maintenance and tube replacement. On the flipside is solid-state technology, a more recent development that requires virtually no maintenance.
By and large, tube amps are noted for their warm, creamy tone. They create distortion when they're overdriven; ideally, a player can roll back her guitar's volume to play clean parts and then slide right into an overdriven lead by cranking back up.
Solid-state amps often get a bad rap for lacking warmth, but their crisp, clean sounds are tough to beat. Many jazzers value solid-state amps since they're hard to overdrive, and those players simply rely on effects for distortion.
Until recently, tube amps were typically more expensive than their solid-state counterparts, and solid-states ruled the basements of underpaid young musicians. But guitarists' demands and the vintage craze have brought the prices of tube amps and solid-state amps to comparable levels.
What do you need? It depends on your ears and your style. One has to admit that tube amps rule the roost these days. Most advanced players know and love the tone of a good tube amp, such as vintage Fenders and Marshalls. There are many companies that make new amps with that "vintage sound" today, so you have plenty of choices and price points to play with. Despite the cool sound, though, high-end tube amps are usually more expensive, more fragile, heavier, and periodically require tube replacement and bias adjusting. Solid-state amps, on the other hand, can be affordable, light, and have a brighter tone overall. Some players dismiss their onboard distortion settings as too "cold," but for many it's a perfectly acceptable way to go. In short, don't get a tube amp because all the pros use them. If you hear a good solid-stater, go with it. When you're ready for a change, your ears will tell you.
Combo vs. Separates
Do you want an all-in-one combo amp, or a separate head and cabinet? This one can be solved easily. For about 90% of all guitarists out there, a good combo amp can do the job. These amps give you your speakers, preamp and power amp, and basic effects in one convenient and relatively portable box. Moreover, there are many types of combo amps. For guitarists who primarily play at home or with a small band, a small combo with one 8", 10", or 12" speaker will do the job fine. Even if you are playing small venues, these amps can do the trick. When you get to a 200-seater, you might want to step up to a 2x12 combo (2x12 = two 12" speakers). There are variations on this amp, with 2x10 and 3x10 setups, but a 2x12 is standard and delivers a fine, beefy tone.
Separate head and speaker configurations are really for working professional guitarists. Unless you're playing a lot of gigs in big venues and know a specific tone you're after, combo amps should be fine for most players. Indeed, you can play a 10,000-seat stadium with a well-miked 2x12 combo. Separates are great for hard rock/metal players who need a lot of stage volume and that imposing "Great Wall of China" look behind them. They are also great for studio players who like mixing different heads and cabinets for new and distinctive tones. But if you're reading this primer, chances are a combo will do just fine.
Wattage is a funny thing, because each amp is so different in how it handles electricity. For example, I once played a 30-watt tube amp that was louder than many 100-watter solid-state amps I've tried. Don't get hung up on wattage. Many younger players want a 100-watt amp so they can tell their friends they got a 100-watt amp. Big deal. That much wattage doesn't mean anything if it sounds like crap. You only need a loud amp if you're going to be gigging in big clubs without a PA or if you play in a heavy-metal band wherein loudness is godhead. But here again, watts aren't everything. When I was a senior in high school, I played a Battle of the Bands contest. My rival showed up toting a full Marshall stack with a 100-watt head and two 4x12 cabs. I, meanwhile, had a little tube combo with 50-watts and one 12" speaker. Running through the PA, his amp totally overwhelmed the sound system and sounded like squat in the school auditorium. My amp sounded absolutely great because it was making the PA do the work. Think about it.
The main thing to know about speakers is that low-watt speakers, like 25-watt Celestions, distort more easily and are often preferred for that hard-rock sound. For a cleaner tone that can be maintained at higher volumes without breaking up, get a 100-watt speaker. Truth is, you can gig for 10 years and never even play at a volume that justifies 100 watts of power. Because low-wattage speakers are easier to overdrive; you can play at a more reasonable volume and get a sweet drive out of 30-watter.
Think again about how you will use the amp and what flexibility it should offer. If you want to be able to step on a footswitch to change between distinct clean and dirty sounds, you need a two-channel amp. It's common to find dual channels, but make sure that one input - that is, the one guitar you're playing - can be directed to either channel easily. Then you can set the gain and EQ settings as you like for each channel. Usually you can look at the amp's face and easily tell which settings are global (for both channels) and which are channel-specific. See if the channels are footswitchable, and if the price includes the switch. You might not even look at the amp's back panel for the first six months you own it, but find out what's back there before you buy. Can the amp take a direct line out for recording or for feeding a PA? Can it drive a second speaker cabinet? Is there an effects loop? A standby switch? Such factors might never be important to you, but you'll eventually get more out of the amp when you know what it can do.
Most amps come with reverb, usually generated by a spring-driven box bolted to the bottom of the inner cabinet. Some vintage amps (and vintage-styled amps) will also come with a tremolo control for that dreamy surf-rock sound. While you can't expect a low-priced combo to have much more than reverb, these days amps are available with full digital effects onboard. This is a mixed blessing. On the one hand, it's very convenient to have your effects right there on the amp, so you don't have to mess with any external stompboxes or rack units. On the other hand, if you decide later you don't like those internal effects, you're stuck with a built-in part you don't want. Make sure you really like the internal digital effects - and make sure they're bypassable - before plunking down the extra money to buy an amp like this.
No matter what gizmos are available on an amplifier, the bottom line is that it has good tone. What is "good tone?" For most of us, that means a clear high-end that's not too trebly, an adjustable midrange that you can tweak to your preference, and a really fat, big bottom end. Bass is so important to good tone, but many guitarists don't think about it enough. As a test, take your current amp and turn the bass all the way down. Your guitar sounds like it's coming out of a crummy AM radio, right? What many top players agree on is that even great guitars need a good, fat bottom to flesh out their tone. Of course, you don't want it to be so overbearing that it's "boomy," but never overestimate the bottom. To that end, compare several amps during your sound tests and see which one delivers the bass goods. My guess is that that's the one to go for.