HOW WE GET THAT GROOVE TUBES SOUND
Guitarists both yesterday and today can be linked by one piece of equipment: The tube amp. With all the strides in transistor amp technology, guitarists still prefer tube amps. Why do tube amp designs sound and feel differently from solid-state? Simply, tubes work differently.
What is a Tube? A tube is an electronic device consisting of a minimum of four active elements: a heater (filament), a cathode, a grid and a plate. All sealed in a vacuum glass enclosure to prevent parts from burning. Once heated, the cathode begins to emit electrons, which flow from the cathode (which is negatively charged) toward the plate (which is positively charged). The grid’s purpose is to control this flow, in effect, acting as a valve.
How do Tubes Work? When the guitar’s pickup produces a small voltage (the result of the string vibrating in the pickup’s magnetic field), this signal is applied to the grid, which causes a large current flow from the cathode to the plate.
Because of this, a correspondingly large voltage now appears at the plate. A portion of the amp’s electronic circuitry, the grid bias control, adjusts the proper voltage setting of the grid. When the grid bias is properly set, the tube is balanced to the circuit, and therefore produces a clean, powerful signal. The plate is connected to an output transformer, which matches the impedance to that of the speaker.
How do Tubes Distort? As the signal emitting from the plate approaches its maximum potential, the tube gradually begins to react less and less to the original input signal. This results in a type of compression of the signal, and the signal becomes cut off or “clipped.” Tube distortion (“clipping”) occurs gradually, producing low order distortion which compliments the original signal, creating a warm sound. This is also why it’s easy to move between clean and distorted tones.