Building your own tube guitar amplifier is a great way of saving money and getting an amp that is exactly to your own spec. There are three main parts to a tube guitar amplifier: the preamp, power amp and speaker. Tube amplifiers are easier to assemble than solid state (transistor-powered) amplifiers because there are less parts. But tubes require more maintenance than transistors. Tube amps have a warmer sound than solid state amps.
Acquire the necessary parts for your amp. You can either purchase a tube guitar amplifier kit (see References 1) which comes with all of the necessary parts, schematic and assembly instructions. This is a smart choice if you are inexperienced with amplifier self-assembly. You can make further savings by salvaging your parts, but this will take you longer. If you are salvaging your parts, make sure that they are all compatible.
Find a suitable schematic. The schematic is a diagram of the interior circuits and parts (see References 2). It illustrates the order in which the parts are laid out in the circuit and also provides information on voltages and spec. If your parts don't come with a schematic, you should find a tube guitar amplifier schematic before you begin assembly.
Inspect the parts for damage and faults. This is especially important if you are salvaging your parts. One faulty part can cause the whole amplifier to cease operating. Look out for rusted terminals and burnt-out tubes.
Prepare the cabinet. Your cabinet's interior should be divided into three sections. The main section is where the speaker is housed. The preamp section should be at the top of the cabinet in a position so that dials and jacks are exposed at the front. The power amp section can be anywhere inside the cabinet, provided that you can wire it neatly to the preamp.
Insert the preamp section of the amp, but don't load the tubes. You should be able to slide the preamp into the relevant section, leaving the front and rear exposed.
Insert the power-amp section of the amp. Make sure that the rear is exposed so that you can wire it up to the other parts.
Install the speaker. There will be a series of small holes around the edge of the speaker. Use these holes to screw the speaker to the interior of the cabinet.
Wire together the three main parts and the remaining components using a soldering iron. Your schematic will illustrate what order the parts are connected. All amplifiers are different, so pay close attention at this stage.
Insert the tubes. It is better to insert the tubes last so that they are not at risk of being damaged during the screwing or soldering stage of assembly, since tubes are very delicate. Your preamp and power amp will have sockets for the tubes, but makes sure are putting the correct tubes in the correct socket.
Set up a well-lit and well-ventilated workshop. An adjustable lamp is useful when soldering, as you can shine it directly on the parts that you're working on.
Even small amplifiers can be dangerous if wired incorrectly. If unsure, consult a professional electrician.