PLEASE READ BEFORE ATTEMPTING ANY WORK.
Ensure you have unplugged the amp from the mains electricity supply. Some amps, particularly those fitted with vacuum tubes, can retain dangerous voltages inside the chassis after they have been switched off and disconnected from the mains supply. Allow sufficient time for voltage discharge and tube cooling before following these steps.
Guitar speakers have large magnets which can affect audiovisual equipment including, but not limited to, television screens and computer monitors. Pick your location carefully and make sure you have plenty of room in which to work.
Speakers must be capable of taking at least as much power as the amp puts out, or you risk damaging them. So, for a single speaker, pick one with a power rating the same or higher than the amp itself. For a twin speaker combo the minimum speaker power rating is half that of the amp and for a cabinet with four speakers it will be a quarter of the amp's maximum power output.
Just as important as power rating is impedance - given in Ohms (written - Ω). If you use the wrong value, then the amp may be damaged. Ensure that your new speaker has the same impedance as the speaker it is replacing. So, if you’re taking out an 8Ω speaker, make sure the replacement is also rated 8Ω. (Note - some vintage speakers are rated at 15Ω, you can use these to replace a 16Ω without fear of damage.)
Make sure the amp is disconnected from the mains supply and you have allowed sufficient time for the tubes (if fitted) to cool down and discharge any residual voltage if you have used it recently.
Check the terminals - are they‘push on’connectors or‘solder only’?
Remove the back panel from your combo/cabinet (where fitted) and make a note of which color wire goes to the + terminal of the speaker.
Disconnect the wires and get them safely out of the way using tape. Next, ensure the terminals are cleaned to achieve the best connection.
Undo the bolts, then carefully remove the speaker(s) taking care not to damage the cone or anything inside your amp. Careful - you may find the speaker is slightly stuck to the front baffle and comes free suddenly. Place the speaker face down on a flat surface.
Carefully insert and bolt in the new speaker (take care when handling so as not to damage the cone). Finger tighten all bolts then tighten them with the appropriate tool, securing diagonally opposite bolts in sequence. Hand tight is fine, this will ensure that you don't bend the speaker frame.
Connect the new speaker according to the wiring diagram you made earlier. Make sure all connections are solid and secure (you may need to tighten the clips using a pair of pliers.) If soldering, take precautions to ensure that hot solder cannot drip on to the speaker cone – it will cause damage. Re-check the wiring is correct!
Once you’re confident that the wiring is correct, plug in and turn on at low volume. Check for buzzes or anything untoward.
When everything sounds OK, put the panels back and you’re ready to go.
Dr. Decibel gives you some hints about breaking-in your guitar speaker
A brand new, out of the box guitar speaker will subtly shift in tone over the first few hours of playing as the fibres within the cone start to relax and become more pliable. Don't worry too much about this change, its natural and many people believe that this improves the sound, making it more 'rounded' and pleasing to listen to.
Some players prefer to speed up this process, this is what is referred to as breaking-in; they deliberately soften up the cone in order to bring the speaker to it's optimum state in terms of tonality.
You'll hear about lots of different breaking in techniques. Some play random noise through their speakers, others prefer to play music through them for many hours.
There's plenty of debate over the technique to use for break in and how long to do it for, but they all achieve the same end, softening up the cone and rounding out the sound. Below is our preferred method.
Before breaking it in it's advisable to warm up the speaker gently for a few minutes with low-level playing or background hum.
turn up the power amp volume to full, and control the level with the preamp gain. Use a level that will be quite loud, but not painful in a normal size room.
Have the bass and mid up full, and the treble at least half. On your guitar, use the middle pick up position (if your guitar has more than one pick up) and play for at least an hour, using lots of open chords, and chunky percussive playing.
This will get the cone moving, and should excite all the cone modes and get everything to settle in nicely. The speaker's tone will continue to mature with additional hours of playing, but this will get it most of the way there.