Amplifiers explained  
When you first try an Amplifier, it’s a good idea to set the EQ. (Equalization) flat, that is the middle area with nothing cut or boosted. This will give you a good starting point to see what the bass and the amplifiers sound like, then add EQ as desired. Make sure the amplifier you choose has enough power to handle what you need it for. Don’t use a small amplifier if you’re playing in a loud rock band and it doesn't make much sense to use a huge ‘Rig’ for a small restaurant gig.
There are two main types of amplifiers, valve and transistor. Sound-wise they react differently in the way they handle and generate distortion. As the input signal increases to drive a valve amp to maximum power, the valves gradually react less and less, producing a type of compression and soft clipping (clipping occurs when the input signal is increased to a level where any further increase doesn’t produce any corresponding increase in volume of the output as the amplifier reaches its maximum power). Transistor amps cut off (clip) sharply, producing hard edges, when maximum power is reached.
Valves produce even order harmonic distortion which is warmer and not as harsh as the odd order harmonic distortion produced by transistors. Valve amps also have an output transformer which ‘saturates’ at clipping levels, transistors don’t require an output transformer. Adding an extension speaker to a valve amp requires changing the tappings on to the output transformer, to match the impedance (load) of the new speaker combination. It’s usually done via a switch or pre-wired into the extension speaker socket. With a transistor amp, adding a speaker automatically adjusts impedance to the new ‘load’ of the speakers and delivers more power. In both cases check the amps owners manual and follow the instructions. There are two basic ways to wire speakers together, in series where you add the impedance together to get the total impedance (load), or parallel in which case the impedance is half that of one of the (identical) speakers.
Only wire speakers together with the same rated impedance and wattage rating. Different brands of speakers differ in their tonal characteristics and replacing a speaker with a different brand could change the overall sound. Smaller speakers accent the top (treble) and large (eg. 15") the bottom end. Valve amps generally require more maintenance. Output tubes should be replaced if the sound appears to be deteriorating. Any other problems (apart from valves) with either type of amp should be handled by a qualified service technician. When purchasing your amp, bear in mind the kind of music and gigs you are going to be playing. Your amp should match the power of the other group member’s amps. A small amp with the sound you are after can always be miked up, a big amp may have to be turned up to get the best sound, possibly blowing away the rest of the band - and maybe the gig.
 
 
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