Decide which type of amp you want to build. Solid state amplifiers (transistor circuitry, no tubes) are more simple to construct and are less likely to break, but tube amps (tubes were used to amplify sound before transistors were invented) generally sound better. You’ll also need to chose between using a guitar kit or salvaging the parts yourself. If you’re using a kit, all of the necessary parts come in one package. If you want to salvage the parts, you may save money but it will take you longer to find all of the necessary parts.
Inspect the parts for damage. If you’ve received your parts in the mail, it’s smart to make sure they aren’t damaged before you begin making your homemade small guitar amp. Check for cracks to the amp chassis, make sure the speaker cone is free from perforations and examine the wires to make sure they are in good condition. You should also receive a schematic with your amp kit. If you don’t have a schematic, you can view them online.
Install the pre-amp into the amp chassis. The chassis should come with the necessary compartments built in. If not, you can make your own by screwing in some wooden slats. Your pre-amp has the input jack and control dials, so the the front panel must be exposed at the front of the amp for easy access. If you are building a homemade small tube amp, the pre-amp will have sockets for the tubes to slot in to. Put the tubes in at the end.
Install the power amp component. This should be second in the chain after the pre-amp. Connect the two by soldering the wires from the pre-amp in to the power amp. There will be signals on each component illustrating where to attach the wires. If you are building a tube amp, the power amp component will have sockets for the tubes to go in.
Install the speaker in to the amp chassis by screwing it to the inside of the chassis. Do this either by screwing it to the inside of the front panel or to the back of separate, smaller ledge near the front of the panel. There will be a series of small holes around the edge of the speaker where the screws fit. Even though you are making a small homemade amp, your speaker will still be able to produce reasonable volume when turned up full.
Solder the speaker cables to the power amp to complete the amplifier signal chain. Finish the job by connecting the power supply to the pre-amp and installing the tubes in their sockets.
Test the amplifier before enclosing the chassis.