Download a tube microphone pre-amp schematic from an Internet resource. A schematic is a diagram of the electrical components involved in the device and how they are wired to each other. A schematic uses symbols to represent electronic components and their relationship.
Use your tube microphone pre-amp schematic as a parts list for your project. Write down each component as listed on the schematic, both the type of part and its specifications, and purchase the necessary components from an Internet retailer. Most pre-amps are simple circuits and require an assortment of resistors, capacitors, audio in-out ports, a transformer for power and potentiometers (knobs) for adjusting gain levels.
Arrange the electronic components on your blank circuit board in the order and location indicated by your schematic. Arranging the components as the schematic shows assures accurate wiring. Bend the connecting pins of each component at a 90 degree angle after you insert them into the board.
Solder each component to the board with your 25-watt soldering iron. Place a portion of the rosin-core solder against the joint of each component's connecting pin and touch the heated tip of your soldering iron to the solder. Allow each soldered joint to cool for five minutes and cut the excess tip off with wire cutters. To keep your board clean and avoid burns, begin soldering at the left side of the circuit and end at the right side.
Draw the connections between components as represented in the schematic directly onto your circuit board using your wiring pencil. A wiring pencil works similarly to a soldering iron. Once heated, the wiring pencil melts a small amount of conductive copper which comes from the tip in a line allowing users to draw connections between components as if with a pen.
Enclose your circuit in a project box, or plastic or non-conductive metal container. Enclosing your tube-microphone amplifier protects the internal components from damage and protects the user from the live circuit. A tube microphone pre-amp necessarily requires direct current and subsequently the circuit should never be plugged unless enclosed.