The basics. As we all know, the electric guitar depends on an amplifier for its sound to be heard, and the amp boosts the signal sent by the pickups. The signal produced by the vibration of the strings through the pickup windings is too weak to drive a speaker. So we need an amplifier and a speaker to hear the instrument.

Put simply, the amp has to draw electrical power from the outside, through the mains (or batteries in the case of "babies" and small, low-power amps). Likewise, the amplifier will let us (in practically 100% of cases) control the EQ and, depending on the model and its particular features, the gain, effects and any other extras it may offer.

Hi-fi or saturation?
An amplifier can be designed to faithfully reproduce the input signal. In other words, to reproduce strictly and accurately the signal we feed it from the guitar or another source. For guitar, this kind of amplification could be suitable for acoustic or classical guitars because of its clarity and definition. For electric guitar playing, it is more common, and advisable, to use amplification designed to enrich the harmonics, gain and warmth of the signal that we originally send to the unit through our cable (the one coming out of the guitar).

Combo versus head + cabinet
Once we've established the need for an amplifier and one or more speakers, we find two basic types.

a) Combo amp. This is the one that houses both the amplifier electronics and the speaker in a single enclosure (cabinet). Combos usually have a handle on top, are more manageable and easier to carry, and as a rule are smaller (in both size and power), although there are some real monsters in combo format. It wouldn't be accurate to say that combos are all entry-level or midrange, because this type of amp design includes some true gems: legendary high-end amplifiers of absolutely professional quality. In short, it is a manageable tool (some more than others) for the studio and the stage.

b) Head + cabinet. As you can guess, this time we have two separate units. The first is the head, the device that amplifies, and the second is the cabinet: the enclosure that houses one or more speakers. It's easy to see why most high-end and top-end amplifiers come in this format. Having two "amplification + speakers" units gives us more flexibility, since we can choose exactly the head with the exact features we personally want. Independently, we choose the cabinet, with the exact format, dimensions and type of speakers we want to run the signal from our head through.

As a general rule, this type of amplifier is heavier and bulkier. Likewise (again, in general) we run into "diabolical" beasts in terms of power, and they are harder to transport. Every hard-rocking guitarist's dream: an amp almost as big as he is. In short, its main role is as a high-power live rig.

Tubes or transistors
Skipping the technicalities, here is a general comparison between tube amps and solid-state amps.

When a tube amp is run at high volume, we hear the characteristic saturation of the tube. We get a warmer, richer sound, a more pleasing feeling of power, stronger (even-order) harmonics and a thick attack. By contrast, transistor amplification, when saturated, produces mainly odd-order harmonics. The result is a more artificial, "unpleasant" saturation to the ear, less warmth and the loss of the characteristic original tube sound.

It has to be said that technology is advancing by leaps and bounds, and solid-state amps have steadily been climbing the ladder. Amp modeling is fully up to date, so many solid-state amps now offer a powerful selection of models, emulating the tubes, amp type and cabinet, not of just one amp but of several, so you can choose the (simulated) amp that suits each piece you play.

Finally, my conclusion is that there are some quite acceptable solid-state amps, even recommendable ones if your sound isn't yet perfectly defined. That is, having several models gives you versatility and lets you "jump from one amp to another at any moment." Still, as a guitarist (personal opinion), I would add that there is nothing like a good tube sound.

Speaker and amplifier compatibility
Tube amps must be matched to the speaker impedance with great precision. A tube amp should never be turned on without first being connected to a speaker, as it can suffer serious damage (to both the transformer and the tubes).
Solid-state amps, on the other hand, are less demanding and more immune to short circuits and open circuits at the speaker output. If we use higher-impedance speakers in this case, we will lower the output level and most likely the distortion. A solid-state amp usually has a label stating the minimum impedance, which is the one that will produce the maximum output and the right amount of distortion.

Channels and extras
Older amplifiers usually came with two guitar inputs, differentiated by their high and low signals. Modern amplifiers (in general) tend to have two or more channels and offer more features. For example, as a standard setup, we can find a "clean" channel, specifically designed to deliver the most crystalline, clean sounds, and a "drive" or saturated channel that gives us the full punch of gain. These channels will have (depending on the case) independent EQ, independent gain (perhaps the clean channel won't have it), and so on. This way we can switch from one channel to the other (most likely with a footswitch / pedal), alternating heavy sounds with mellow ones as we change channels.

As for the extras built into our amplifier, we may find anything from a built-in electronic tuner, a multi-effects unit (chorus, wah, flanger, delays, compressors, etc.), preamps, MIDI connection options, tube amp simulators, cabinet and speaker simulations, channel-switching pedal jacks or complete pedalboards that also control the effects units, outputs for optional cabinets (mono or stereo), and inputs for amplifying external sources such as a CD player.

Summary and final conclusions for beginners
The range on offer is so large that, if you look carefully, you could find several suitable amplifiers of different types. Overall, I think a solid-state amp with good modeling could be the easier way to start, even through the "intermediate" stages of a player's development. Another option would be a solid-state amp plus a multi-effects unit with amp and cabinet simulations. These options can make for a cheaper purchase and offer some versatility to learn to identify the sounds you like most, so you are surer of the type of amp to buy in your second step. Finally, my conclusion is that after trying many amplifiers, there is nothing like a good tube amp to which you add your favorite effects (a few or none). Personally, I think it's better to find a personal, distinctive sound: less but better (in both amplification and effects). Obviously, some guitarists will hold the opposite opinion; there's no accounting for taste.

The choice: a tube amp, or an excellent effects unit with realistic amp simulations (which would make it easier to play direct, with headphones, without losing quality and at more moderate volumes, if you play at home or in a studio, for example).

Transistors

  • Cheaper
  • More durable
  • Less maintenance
  • Greater versatility
  • Poorer sound quality
  • No warm-up required
  • More artificial saturation

    Tubes

  • More expensive
  • More delicate
  • More maintenance, and tubes must be replaced as they wear out
  • More distinctive sound
  • Better sound quality
  • Tubes need to warm up
  • Warmer saturation and gain