The development of guitar amps is traceable back to the 1950s, when many classic Fender designs came on to the market. In an odd reversal of the usual trend, this valve based technology is preferred by many players, and consequently many older amps are now very valuable.

TYPES OF AMPLIFIER:

• Valve (AKA tube amp)
  

• solid state electronic

• digital modelling

Sometimes these types are combined to form a hybrid, where two different technologies are used together.

The speaker, usually 8", 10" 12", or multiple speakers is a vital component in the sound. Sometimes there is a separate speaker cabinet, sometimes amp and speaker are together in a combo amp. Speakers are often upgraded to improve the sound, and this is a relatively simple job in many cases.

Power ratings: common output in watts - 30w , 50w, 60w, 100w. A practice or recording amp for home or studio use could be 10w or 15w. I find most gigs only need about 30w amps, maybe 50w if there is a drummer.

If you use a combo amp and need more volume another option is to add an extra speaker cabinet, although you should check the impedance or ohm rating of both the amp and the new cabinet.

The high end of amps in terms of sound quality and durability include:

Fender, Marshall, Vox, Matchless, Bad Cat, Cornford, Mesa Boogie.

Boutique amps are often hand-wired: Carr and Victoria are two of the most highly rated. This is one area of music where it definitely pays to buy the best.

Fender amps from the 1960s or Blackface (from the control panel) are highly regarded, Silverface (1970s) less so, but they are still very well built.

The quality of valves used is very important, and these are now cyrogenically treated to improve the sound in some cases. Speakers are also upgraded from the original factory models in some cases. In the UK there are companies such as Watford Valves, who supply spares and upgrades.

There has always been a thriving industry in modifying and upgrading amps, which is how Mesa Boogie started in business. Some cheaper Chinese-made valve amps are improved by tweaking components in this way - although, a word of caution: Valve amps contain lethal voltages!!! - leave it to an expert.

A seperate category, typified by the AER combo amps. Acoustic guitars need a different approach in terms of sound, and using a normal valve amp won't work that well. The solid state nature of these amps means less maintenance is needed - and they can often be used with a microphone as well, making them ideal for small gigs in a cafe environment. The downside is a very clinical and unresponsive nature, with none of the warmth of valve amp tone.

For the acoustic / folk performer, this is the preferred option. The less sound coloration the better. Bose L1 line array systems are well regarded too.

Schertler make good acoustic amps - at the moment I'm using a Unico amp. It's good for vocal mics too.

The type of pickups on different electric guitars is also important, and getting the amp and guitar to complement each other is a really complex issue. For this reason, many famous guitarists use multi-amp rigs, using different tones from a number of amps.

To get a rock or blues tone some distortion is common, and this can be created with a gain control. Gain helps create a musical sustain and distortion. Many valve amps work best when the output valves are working hard, as well as the preamp valves. This means a low -powered amp is often preferable,as it can be driven hard in situations where a 100-watt amp would be too loud.

A classic combination would be the Hendrix sound - Marshall amp and Fender Stratocaster together, or the Eric Clapton Les Paul and Marshall combo sound. A Fender Telecaster works great with Fender Twin, Blues Deluxe, Deluxe Reverb amps, among others. Associated with many country players.

Carlos Santana uses a PRS guitar with Mesa Boogie amps to get great sustain.

Guitar Player magazine (USA) is very good for amp reviews.

In the UK Guitarist magazine also does very in-depth reviews.

Personally, I like Fender Blues Deluxe, Deluxe Reverb amps for affordable good tone and projection - partly because they suit blues and jazz styles well.

There are two main ways of improving valve amps, and they are both easy - part of the appeal of the whole design.

• Change the valves - a matched set of new valves is sometimes very effective. Chinese-made valves are not highly regarded, in fact that is being polite! Replacing them with high quality valves by Groove Tubes etc. can work wonders.
• Change the speaker - many cheaper amps use substandard speakers. Replace with Celestions or JBL etc and the sound can be dramatically improved.