Valve amplifiers, or tube amplifiers as they are more commonly called, use vacuum tube technology to amplify an audio signal. A stereo amplifier is any amp with two or more speakers. When incorporated into a tube guitar amplifier, the double speaker configuration allows for phase shifting between speakers. This enables you to use effects such as chorus, delay and flange. You can make your own valve stereo amplifier using an amplifier kit. These include all of the key components as well as a cabinet, wiring schematic and assembly instructions.
Source your kit. You can order it online from a variety of suppliers. Many kits emulate the design and configuration of iconic stereo tube amps. For example, the Classic Guitar Amps website lists a Fender Twin-style amplifier kit. (See References 1)
Inspect your parts and read the schematic. Before you begin assembling your amp, check the parts for damage. The supplied schematic is the map of the amp's interior. It illustrates the layout and configuration of the circuits.
Load the circuit board. This where the signal processing takes place. Your tube bases, capacitors, resistors and diodes go here. Follow the schematic when mounting the components. Typical amp kit circuit boards are pre-drilled.
Wire the turret board. Once the board-mounted components are in place, solder them from the base of the board.
Build the amplifier chassis. Your amplifier has two transformers: a power transformer that converts the guitar signal into an electrical current and an output transformer that adds voltage to the current before driving it to the speakers. Mount each transformer in the square hole on the chassis. Make sure the solder lugs are level before soldering the transformer to the chassis.
Mount the preamp inside the chassis so that the front panel is exposed at the front. Wire the preamp and connect the transformers as per your wiring schematic.
Mount the power amp alongside the preamp and solder a wire each to the two output terminals. Thread those wires through the hole in the chassis. Connect each preamp potentiometer to the relevant input terminal on the board. Do not install the tubes yet.
Load the chassis. The completed chassis contains the circuitry, preamp and power amp. The transformers are mounted on the exterior.
Fit and connect the speakers. Screw each speaker into the support struts that run horizontally along the inside of the top and bottom panels of the cabinet. Tighten each screw equally so that the speaker sits flush against the two struts. Pull the two wires connected to the preamp out of the hole in the chassis and wire one to each speaker.
Mount the tubes. Put on a pair of latex gloves to protect the glass from the oils on your hands. Slot each tube into its enclosure as per the assembly instructions.
Enclose the cabinet. Screw on the front grill and back panel.
Test the amp with a voltmeter to ensure that all of the resistors are working.
Exercise caution when building any type of amplifier. These devices carry potentially deadly amounts of current.